Preamble Hello. Given the tedious and predictable hegemony of the Premier League's bigger clubs, it's inevitable we'll scour hopefully for weaknesses, like subscribers to Heat magazine: this much cellulite on Angelina Jolie, say, or rumours that Brad Pitt still soils the bed if he has too much Gym Syrup. Yet this season Chelsea's weakness has been obvious: their home form.

They have seven wins out of seven away in the league but only three at home. Not since the Second World War have they gathered such a low percentage of their points at home (36), although of course that should balance out by the end of the season. You'd fancy them to get all three against a weakened Arsenal side today, but then Arsenal's need is even greater: they are ten points behind Chelsea, and if they lose they are out of the title race.

Chelsea (4-1-3-2) Cech; Bosingwa; Ivanovic, Terry, Ashley Cole; Mikel; Ballack, Deco, Lampard; Kalou, Anelka.

Subs: Hilario, Malouda, Bridge, Ferreira, Mineiro, Alex, Stoch.

Arsenal (4-4-2) Almunia; Sagna, Gallas, Djourou, Clichy; Denilson, Fabregas, Song Billong, Nasri; Adebayor, Van Persie.

Subs: Fabianski, Vela, Ramsey, Silvestre, Wilshere, Bendtner, Gibbs.

The team news poses a few questions. Chelsea's collection of outfield players would suggest a switch from their usual 4-1-2-3 to 4-1-3-2. That's interesting, not least because Chelsea came from 1-0 down to beat Arsenal 2-1 at home last season only when Avram Grant made that exact tactical switch (to chants of "You don't know what you're doing" and "Baron Greenback is a banker"*). I miss Avram Grant.

Arsenal, meanwhile, prefer Johan Djourou ahead of Mikael Silvestre. Two reasons: a) he's good in the air and b) he's not Mikael Silvestre. Adebayor and Sagna are fit.

*Okay, one of these might be a big, obese lie.

Tactics watch Andy Gray reckons it will be the usual 4-1-2-3/4-1-4-1, with Deco wide left and Kalou right. As he has published a book on tactics second only to Jonathan Wilson's*, I'll take his word for it.

*No, I don't know of any others for over-12s either. And there won't be any now because Wilson's, which really is marvellous, has closed the market.

Prediction: Chelsea 1-2 Arsenal You heard me.

1 min Arsenal kick off from left to right.

2 min "How much better are Chelsea under magician Big Phil than under dear old Uncle Avram?" devil's advocates Gary Naylor They are easier on the eye, but the results haven't jumped forward very far have they? And isn't the criticism of Professor Wenger that his pretty patterns don't actually deliver the points? Uncle Avram got an unfair press because he wasn't Jose, Big Phil, 'Appy 'Arry or any of the other quote-machines the journos love." If Mourinho had done Grant's monosyllabic press conference, it'd have been hailed as Cloughish genius.

3 min A typical thud-and-blunder start. The atmosphere sounds fantastic. I'm still not sure what system Chelsea are playing. Kalou is roaming a lot, but Deco is definitely playing to the left of centre. I think it is their usual 4-1-2-3, but Kalou seems to have a lot of freedom to join Anelka: in that attack, he runs across the line onto Deco's through pass and is wrongly given offside.

5 min It's all Chelsea thus far. Anelka goes down in the box under a challenge from Fabregas, but he got something on the penalty and the only half-appeal came from Martin Tyler in the Sky box.

8 min At the moment Chelsea's physicality is too much for Arsenal, who have yet to get into the game.

9 min "Hi Rob. In the first minute you wrote 'Arsenal kick off from left to right'. Isn't the ball supposed to go forwards, not sideways?" says Robin Hazlehurst, setting the tone for another afternoon of defiantly untickled ribs and lost serotonin.

10 min The first corner goes to Arsenal, but it leads to Chelsea breaking, outstandingly through Kalou, to eventually win a corner of their own. It comes to nothing.

11 min Deco hasn't been in the game much yet, which is the problem in the system. I still don't see how you can play him, Lampard and Ballack in a 4-1-2-3

12 min Arsenal have come into the game a bit now. Van Persie breaks clear down the left and his low, driven cross is put behind at the near post by Ivanovic. It's cleared and then switched to the other side, the right, where Adebayor has loads of space. His cross is taken off the head of Van Persie by Gallas eight yards out and screws acros to Fabregas beyond the back post. His low, slightly scuffed shot rebounds off the squatting Cech and away.

14 min Fabregas really gets hold of a 30-yarder but it's straight at Cech.

15 min I've been accused of many obsessions over the years – myself, that booze, myself, Her, myself – but this is a new low. "Good God man you're obsessed with formations," says Eoin Reynolds. "As the grey-haired wise one John Giles would say, the formation doesn't matter if your players are good enough and they know what they're supposed to be doing." Here's a formation: 2-2-2. That's the number of fingers I'm insouciantly flicking in the direction of tacticphobes today, tomorrow, and forever more.

18 min The jet-heeled Bosingwa scoots brilliantly past Nasri and Clichy but, with all sorts of options in the box, he sees tomorrow's headlines and thrashes horribly over.

20 min Presumably in an attempt to get Deco in the game more by reshuffling, Kalou has gone up front now, so the formation is 4-1-3-sorry.

21 min One thing about Arsenal is that, no matter how poor their form, their youngsters are so cocky that the challenge of a big away game will never scare me. If anything it will rouse them: the moral ground is potentially so much higher in Manchester, Liverpool and Chelsea than anywhere else in England.

24 min Lovely move from Chelsea. Ballack plays a pass down the right to the marauding Bosinga, whose first-time cross finds Lampard, on the run, 15 yards out. His flashing header is too close to Almunia, and comfortably saved, but it was beautifully constructed.

25 min "Talking of tactics, the coach of my school football team apparently hadn't heard that the pyramid had been inverted, as we played a 2-3-5," says Mac Millings. "This was in the '80s. The 1980s. I was one of the unfortunate 2. On the plus side, it kept me busy."

26 min The switch to 4-1-3-2 has brought Chelsea's full-backs into the game offensively, as it must, but Cole seemed to lose something under Mourinho and is nowhere near as dangerous or confident going forward as Bosingwa.

28 min Gallas takes Kalou down on the edge of the box. At first glance I thought he'd got the ball, and Arsene Wenger is furious, but replays show it was a really good decision from Mike Dean. The free-kick is in the D, perfectly central, and Ballack's clipped effort goes into the top of the wall: Adebayor's head, to be precise.

29 min "Re 15 mins, Johnny Giles is right," says Gary Naylor. "Every British fan knows that formations and tactics don't matter, as the sages of radio phone-ins prove day after day. To overcome the organisational and technical challenge presented by opponents, all that's needed is PASSION! If only England players had a bit more of this, the last four World Cups would surely have been ours."

GOAL! Chelsea 1-0 Arsenal (Djourou og 30) Johan Djourou, brought in for this game ahead of Silvestre, scores an own-goal. Yet the real fault lies with Manuel Almunia. At the end of a sustained piece of Chelsea pressure, he caught a corner and, instead of cooling things down, threw it straight back to Chelsea on the right. Two passes later Bosingwa was free on the right, and his magnificent low cross was turned in at the near post by the stretching Djourou. It's hard to blame him, because he had no idea what was behind him (as it transpired, Gallas would probably have got it) and had to play it. Andy Gray uses the cricket term "corridor of uncertainty" and that's exactly where that cross was: in between defenders and goalkeeper, and fizzed with real pace.

33 min Chelsea are rampant, Arsenal are ragged, and only a wonderful challenge from Sagna denies Kalou eight yards out as he runs onto Deco's mischievous through pass.

34 min Action at the other end now, as Van Persie draws a very good diving save from Cech with a scuffed, off-balance right-foot volley that was probably sneaking in at the far post. He did really well to get a shot away there. Moments later Denilson dives laughably in the box but gets away without a yellow card.

38 min "In case anyone read the Manchester derby MBM and is worried about me, I'm still on a bus, in traffic somewhere in Maryland," says Emmett Williams, proving that there are other things to be obsessed about rather than formations.

39 min The game has calmed down after that little flurry, and you suspect both side would take half-time now so that they can reappraise things.

40 min Adebayor hasn't had a kick by the way. I'm not sure how fit he is, as he was a doubt for this game.

41 min Chelsea have reverted to 4-1-2-3 - which paradoxically is probably less positive a formation than 4-1-3-2, at least as they play it - since the goal.

44 min It's drifting towards half-time. Anelka nearly breaks free onto Ashley Cole's long, angled pass. He doesn't.

45 min Two minutes of added time. "Did you see who was the most indignant Chelsea mercenary after Denilson's sniper-attack felling?' says Manjinder Sidhu. "Yes, Michael Ballack. Who said Germans don't have an enviable sense of humour, eh?. That should be put in a song by Alanis Morissette or something." Ballack did go ballistic, demanding that Denilson be given a yellow card or at least a Two Pints Of Lager And A Packet Of Crisps boxset for his sin.

Half time: Chelsea 1-0 Arsenal Chelsea lead deservedly after a decent half. Arsenal had more shots, both on goal and on target, but most were from distance and Chelsea had the more dangerous openings. The decisive one came when Jose Bosingwa's devastating cross was turned into his own net by Johan Djourou. See you in 15 minutes.

Half-time chit-chat "Isn't the footballing equivalent of cricket's 'Corridor of Uncertainty' the 'Position of Maximum Opportunity'?" says Gary Naylor. "Getting the ball into the POMO was the objective of Graham Taylor and other devotees of Charles Hughes's approach to tactics - and they are much derided in the bright and shiny Premier League. Sometimes, just sometimes, hitting the POMO is the right tactic - though I bet Arsene knows otherwise."

Surely the POMO is a shifting space, no? I suppose the COU is also a shifting space but essentially it amounts to the same thing: the space in between keeper and defender. In fairness I don't really know that much about the POMO, intractable aesthete that I obviously am.

Christopher King takes stick. Waves it in my direction "I see your following the lead of andy gray in blaming almunia for the

goal. may I point out that over the years one of the features of

arsenal's play has been the ability to put the ball in the

opposition's net in moves direct from their opponent's corners. the

fault lay with the arsenal player he threw it to who didn't shield the

ball and consequently lost it." I don't usually disagree with keeper-led counter-attacks, obviously, and Bramall Lane 1992 still has a little place in my Little Book of Knee Trembling Moments, but you have to be conscious of the temperature of a game, and at that point Arsenal were being overrun. It was dying out for him to give them a breather. And his throw was too firm, so it skipped away from the man (Denilson?). All this, I should stress, is only my humble one, and I may be and probably am wrong.

The other Premier League scores today by the way, were:

Spurs 0-1 Everton

Portsmouth 3-2 Blackburn

Robinho 0-1 Rafael

46 min Chelsea kick off. It's hard to see what Arsenal can do here, beyond the usual. Certainly tactical changes aren't a big thing in Wenger's world, not since the days of regularly bringing on Vivas or Grimandi for Bergkamp if 1-0 up, back in the late-90s.

47 min Chelsea have resumed in 4-1-2-3 shape. "The formation seems to be changing faster than you can say Emmanuel Adebayor," says Eoin Reynolds. "Are you sure you aren't just getting confused by the players running around the pitch?" Well I still don't understand the Usual Suspects, having watched it 666 times, so it's entirely possible.

49 min Deco's simply delicious reverse pass frees Cole on the left in the box, and his cut-back is cleared desperately by Djourou. Chelsea have dominated possession since the break. If they really want a second goal it's there for them, because they are significantly superior to Arsenal today, as I predicted before this game.

52 min Lampard fires just wide from the edge of the box. Kalou tried to stab a pass in behind for Anelka; it was blocked by Djourou and, as it broke loose, Lampard arrived on the scene but scuffed his shot wide of the right post. By his stratospheric standards, that was almost a sitter.

SPECIAL MESSAGE FOR MR EOIN REYNOLDS Chelsea appear to have once again returned to 4-1-3-2.

56 min Chelsea continue to dominate. Arsenal haven't going at all this half, and it can't be long before a change is made: maybe a straight swap for Adebayor, who doesn't look fit.

58 min I feel sorry for Djourou, who has actually had a really good game and scoots across to stop Deco reaching a nice scooped pass from Anelka.

GOAL! Chelsea 1-1 Arsenal (Van Persie 59) Where the hell did that come from? Arsenal hadn't had a kick in the second half but they certainly have now. Denilson stabbed a pass through to Van Persie, who was clearly offside, on the edge of the box and he thrashed it high past Cech with his weaker right foot. It's an emphatic finish from Van Persie, who has been excellent today as a lone striker (yes I know Adebayor is playing), but he looked to be not just a bit offside, but miles. That's an appalling piece of officiating, but don't forget to respect it.

61 min Terry is booked for a two-footed challenge on Sagna. That could easily have been a red card if he wasn't the England capt- sorry, if Mike Dean had judged it differently. Terry went low, and that saved him, but he had both feet off the ground and with studs showing.

GOAL! Chelsea 1-2 Arsenal (Van Persie 62) Fitba? Bloody hell. Arsenal are in front! Fabregas drives a long, diagonal free-kick from the left which is headed back across goal by Adebayor, and Van Persie spins to drive it through Lampard's legs, across Cech and into the far corner. It's an outstanding, instinctive finish, and a truly staggering scoreline given the flow of the game.

63 min To pass the time in the Guardian office this morning, between slapping each other on the back, we concurred that Van Persie place in the pantheon was seriously compromised by his record against the big clubs. Football expertise, right here.

66 min Chelsea are shell-shocked, and frankly you can't blame them.

67 min "Who's this Boswinga bloke Andy Gray keeps going on about?" says Archi Campbell. "Graham Taylor's mentioned him too. Is Pleatitis contagious?" Now, now: that's my colleague you're talking about. We're pals*.

*We're not pals. We've never met, obviously. In fact, apart from football, I can't think of a single interest we might share.

68 min A brilliant, zig-zagging run from Clichy is ended cynically by Ivanovic on the edge of his own box. My flabber is gast that he hasn't been booked for that. Van Persie, on a hat-trick, welts the free-kick a few yards wide.

70 min Chelsea substitution: Mikel off, Malouda on. So now it's 4-2-1-3 with no holding midfielder. My head hurts.

71 min Chelsea are gathering momentum again, and Cole's driven cross from the left of the box falls a couple of yards behind Kalou.

72 min Camera cuts to Drogba in the crowd, headphones on and pouting like a diverticulitis-ridden Victoria Beckham. He's suspended because of that coin-throwing nonsense, of course.

74 min A delicious exchange between Adebayor and Van Persie on the edge of the box ends with Denilson crossing wastefully from the right.

75 min Adebayor has come to life now and, though Chelsea are having much of the ball, Arsenal carry real menace on the counter. Maybe too much: Arsenal are pushing as many as five players forward in attack, evoking memories of their (alleged - I didn't see it) naivety in the 4-4 draw against Spurs.

77 min Here's Niall Mullen. "I once stood in a lift next to David Pleat. It was one of my six degrees of separation from you Rob. Now I'll have to start stalking Marina Hydr. Again." The best thing about this is that our man Mullen got so excited about sharing his deviant obsession with the twos of people reading this that he didn't even spell Ms Hyde's name correctly.

78 min Marie Meyer wonders whether Chelsea are flat-track bullies, having tonked the rubbish all season but struggled at home to the bigger sides. I think there is something in that, particularly when they are without the sometimes irresistible force of Drogba and Essien. By the same token, wonders Patrick Crumlish, "Are Arsenal small-game bottlers?"

80 min Chelsea are preparing Miroslav Stoch, who has never played for the club before. Meanwhile, Deco slams over from 25 yards.

81 min Stoch, a 19-year-old Slovakian winger, has replaced Deco. I have no idea what this means tactically.

82 min "I met and spoke with Derek Dougan once at Wolverhampton train station," says Roger Lawcock. I honestly don't know whether to laugh or cry at that tragicomic gem.

83 min Bendtner comes on for Adebayor.

85 min Clichy robs Bosingwa and is clattered by Ivanovic, who is booked. That should have been his second yellow, but I suppose he might not have made that challenge if he was on one. I mean on a yellow, not on one.

87 min Malouda hammers a bouncing ball high over the bar. If this was another team defending their lead in this way, you'd say they were fairly comfortable. But this is Arsenal so you can't take anything for granted.

89 min This result would be a great one for Arsenal, but probably an even better one for Manchester United and especially Liverpool.

90 min There will be four minutes of added time, but Chelsea have no momentum at all. Ivanovic gets away with what should have been his third yellow card of the afternoon, when Bendtner tries to knock it round him and run. Ivanovic took a deliberate step to his right to send the pink-booted nugget flying.

90+1 min Bendtner robs Bosingwa and plays it inside the defence for Denilson, running through on goal. It's a glorious chance, but an excitable first touch is too heavy and Cech is out like a shot to smother the, er, shot.

Full time: Chelsea 1-2 Arsenal Greavsie was right: it really is a funny old game. Chelsea looked as comfortable at 1-0 as you can ever be in one of these top-four contests, but back-to-back goals from Robin Van Persie - the first offside, the second superb - turned the game on its head, and after that Chelsea looked disturbingly clueless. Arsenal, seven points off the top, are back in the title race. I'm not sure who will be happiest with this: Arsene Wenger, Avram Grant or Martin Tyler. Thanks for your emails. Bye.