A crazy game of football to watch, a difficult one to analyse. Two open, attacking sides produced a wonderful game for the neutral, but one that will probably leave both managers absolutely fuming – Wenger because his side were awful and conceded poor goals, Guardiola because his side threw away a 0-2 lead.

Wenger went with his standard line-up, but with Arshavin deployed on the right, Nasri on the left – presumably because Nasri is slightly better defensively and therefore better against the Alves-Messi combination down Barcelona’s right.

Barcelona played Keita ahead of the more defensive option of Yaya Toure, meaning they had the flexibility to switch to the 4-2-4ish shape they’ve played in recent matches. Indeed, the shape they played was probably a mixture between that and their more established 4-3-3. Ibrahimovic was the centre-forward, Messi just off him, Pedro certainly wide-right – but then Keita seemed to shuttle between a central midfield position and a left-wing position, similar to how Ramires plays for Brazil. Keita played a more defensive role than Iniesta did against Stuttgart (a) as he is a naturally more defensive player and (b) Stuttgart fielded two central midfielders, so it was 2 v 2 in the middle, whereas Arsenal play with three, meaning Keita had to make sure Barcelona were not outnumbered in the middle.

Have you ever seen a side start a big game as well as Barcelona started tonight’s match? Within the first quarter of an hour they had already forced Manuel Almunia into five saves, and had a couple more shots blocked. How Arsenal went in 0-0 at half-time, it’s difficult to understand.

The most astonishing thing about the opening exchanges was quite how intense Barcelona’s integrated pressing was. The fact they played with a system that effectively featured four forwards meant that Arsenal’s defenders were all faced with a yellow shirt pressing them immediately, and the key was that Barcelona pressed as a unit, rather than as individuals. They may be renowned for their skilful attacking play, but Barcelona defend from the front better than any other side in Europe.

The often-cited problem with pressing like this is that you can’t sustain it for a whole game, and perhaps this was apparent again, for Barcelona blatantly fell away towards the end of the game. But they were certainly able to keep it up for the first half – simply because the pressing itself was so effective and won the ball so many times. They had 70% of possession in the first half, and therefore they spent much of the half passing the ball around casually rather than pressing.

Arsenal were guilty of leaving too big a gap between their ‘lines’ (Qique Sanchez Flores, whose Atletico team beat Barcelona two months ago, advised that ‘making it hard for Barcelona to find players between the lines’ was the way to beat them) – they should have been squeezing the play in front of their defence, but a lot of the time when they didn’t have the ball, Arsenal’s midfield was closer to the forwards than to the defence. They simply gave too much space to Barcelona in the opening period.

Another stark contrast was whilst Barcelona were defending with effectively nine and half outfield players (Ibrahimovic isn’t a great presser), Arsenal were defending with more like seven. Bendtner wandered around aimlessly when the ball wasn’t near him, Arshavin never looks bothered about protecting his full-back – and Nasri and Fabregas contributed a ‘half’ each – both putting in a couple of decent tackles but simply not pressing as intently at their opposite numbers were.

The problem with switching between a 4-3-3 and a 4-2-3-1 is that the roles of the wide players changes only slightly in terms of position, but hugely in terms of actual role. In a 4-3-3 the wide players are essentially forwards – their main job is to pressure the full-backs and track them if necessary. For those players in a 4-2-3-1, there is one fewer player behind them, and therefore significantly more defensive work from them is needed. They are a second line of midfield rather than a line of forwards. Nasri has the desire but not the defensive ability – as for Arshavin, the fact he was fielded on the right surely points to the fact that even Arsene Wenger doesn’t think he’s up to it defensively.

In a sense, Arshavin going off injured was the best thing that could have happened for Arsenal. He was replaced by the energetic Eboue – and whilst the Ivorian didn’t have a great game, he did provide the running, the determination and the work rate that Arsenal desperately needed when they were being thrashed in the first half.

As mentioned earlier, Arsenal’s main problem was that they left too big a gap infront of their defence – Jens Lehmann said at half-time that their defence needed to push up in the second half. And that’s essentially what they did. Sadly, this left them open to the threat of Barceona playing balls over the top, and sure enough Ibrahimovic scored twice in almost identical circumstances – a long ball chipped into Arsenal’s left-hand channel, and Ibrahimovic finished twice.

Did the Arsenal plan of pushing their defence forward fail? On one hand, of course it did – they conceded two goals by doing it. But bizarrely, it was probably still the right move – those were amongst the only opportunities Barcelona had in the second half. Ibrahimovic’s excellent finishing was the reason Barcelona scored in the second half – the chances weren’t any more blatant than the countless ones they missed in the first half. The goals also came as a result of individual errors by Almunia and Vermaelen – whereas the chances in the first half came because Arsenal were all over the place as a team. (Incidentally, both the goals also game as a result of a lack of pressure from Arsenal on the player in possession – for the second, in particular, they simply allow Xavi all the time in the world to pick out a pass).

But pushing the defence up also squeezed Barcelona in the final third and broke up their attacks more easily, meaning Arsenal saw more of the ball themselves. OK, the first half was a draw and the second half was too – but in terms of dominance, Arsenal were ten times better off in the second period.

Wenger’s decision to send for Theo Walcott was a brave – and inspired – move. Despite how it may have looked, Maxwell is not a slow player – just Walcott is supremely quick. He constantly got in behind the Brazilian both with and without the ball, and he lifted both the crowd and his fellow Arsenal players. There will be inevitable calls for Wenger to play him from the start against Barcelona, but it might well be that this is the best role for him – coming out later on in games. Assuming a vaguely similar pattern of play in the second leg, Arsenal will need to weather the storm early on (perhaps meaning Sagna and Eboue on the right) before unleashing Walcott once Barcelona’s (makeshift) defence tire.

Credit to Wenger for rescuing the situation, but on another day Barcelona would have won the tie by half-time. Arsenal need to learn their lessons from this game if they are to progress: they need to defend from the front as a unit, they need to hold a higher defensive line, and they must field one more defensive-minded player. If they play like they did today at the Nou Camp, they will suffer the demolition job they were fortunate to avoid tonight.

Want more Arsenal v Barcelona analysis? Check out these passing statistics.

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