My hero, it transpires, is a man named Grubby.

Grubby's inferior human name is Manuel Schenkhuizen, and he hails from the Netherlands. He's mild-mannered and pleasant, as far as I can gather, and he's atypically good at StarCraft 2. He's a genius at it, a real pro. He's not as atypically good as some of the other pros gathered in Versailles for the European leg of Heart of the Swarm's Global Launch event, though. The pre-match chatter suggests that Grubby's not going to win tonight's competition. It's a four man affair composed of two semi-finals (each built of three games each), which are capped with a tense three-game decider. Grubby's good, but he's going out in the first round.

This competition is how Blizzard's chosen to let StarCraft 2: Heart of the Swarm loose upon the world, and it feels like a pretty good idea. Two years have passed since Wings of Liberty touched down, and Blizzard's RTS has made the most of them. That's two years of ingeniously asymmetrical warfare, in other words, of bewildered eSports articles in the mainstream press - and sometimes, admittedly, the gaming press. Two years of debates about whether this unit's OP or that race is imba, of tech strats and of build orders. It's hard not to look around Versailles tonight, to see all the moving parts - the crowds, the bunting, the stores shifting glossy copies of Sarah Kerrigan-fronted Risk - and feel like Blizzard's engaged in a deeply elaborate game of StarCraft itself. Squint and you might sense you're watching an RTS match being comprehensively steamrollered by a company that churns out blockbusters with an astonishing degree of confidence. Why's everyone so excited? Why did so many people travel from so far to be here? What's the build order that builds you this?

It's Grubby!

On that front, it's worth remembering that StarCraft 2, for all its intricacies, appeals to players and audiences alike because it's, y'know, pretty entertaining. It's fun to build bases and create units, and it's fun to then chuck those units at your opponent's base. StarCraft's wonderfully elegant in its interlocking parts, and yet surprisingly able when it comes to generating human drama. It's a game of clicking on tiny little soldiers, but it's also a game of grand psychological feints, and while you can plan your approach, the whole enterprise has an endless capacity to surprise you. To shock, even. All of which brings us back to Grubby.

"Aww, he's a fan favourite", explains my friend as we enter the auditorium before the first game begins. "He's just a really nice guy." And this, it turns out, is just a really nice venue. Bright lights skitter across the domed ceiling of the Palais de Congres, while logos loop and mass on monitors. The stage itself looks a bit like it's been prepped for an am-dram production of The Wrath of Khan put together by drunken stone-cladders. There are three desks set up bridge-of-the-Enterprise style, and they're covered with moulded plastic that turns them into piles of unconvincing alien rubble. In the center are the casters: quick-witted commentators skilled at bringing an often mysterious and always rather deep game into vivid focus. On either side of them sit the competitors themselves.

Grubby's up first, and he'll be battling Ilyes "Stephano" Satouri. Stephano's a local hero - well, he's French, anyway - and I'm told he's something of a lady's man and a bad boy. He's the favourite tonight according to a few people I chat to, and perhaps this is visible in that quiet swagger, in that amused, lip-jutting turn of the mouth. He's beaten Grubby in the past. He's beaten him, what, 25 times to two or three? What's a few more games, eh?

That's all very telling, but the Belgian guy seated a few seats down from me has the coup de grace: Stephano turns twenty at midnight tonight - exactly when the competition should wrap up and when Heart of the Swarm will go live on European servers. Twenty! A big day for Stephano and he's ready for it. He's going to win.

Except he doesn't win. Oh, StarCraft. The first game of the evening provides a truly brilliant upset: a dazzling opener, and suddenly everything's in the air.

It's Zerg against the Protoss on a fairly large map. Stephano's the Zerg, and even that feels like an indicator of imminent victory, since Heart of the Swarm is all about this race of hatchling man-killers and many-toothed, many-spined, many membraned horrors. You need a lot of bases when you're a Zerg, and Stephano makes an early lunge, going one base up on Grubby, who's still getting his resource game moving. One base up this early probably isn't good.

Widow Mines - useful but not very pleasant.

But Grubby's made an early lunge, too, and Stephano hasn't noticed it. Grubby's lodged a probe deep within Stephano's territory - a lot of the talk around this most nuanced of sci-fi battlers has the hot breath of Sid James lingering over it - and it allows Grubby to launch an early DT rush on Stephano's hatchery. DTs - or Dark Templars - are deadly but costly: they can take an enemy out if you launch them at the right moment, but if your rival's put up proper defences you'll be rebuffed. Ouch.

Stephano's wide open, though. It's all over rather quickly, and the crowd seems stunned for a few seconds. Grubby's rolled right across Stephano, and he's done it with an astonishingly audacious strategy - an earlyish lightning strike that, had it failed, would have left him wallowing in terms of his economy. Bold! "Grubby's a very original player," says somebody nearby - by this time, on this evening, the crowd and the commentators have all started to sound alike.

After that first game, the casters still aren't betting on Grubby, though, and you can kind of see why not. The second game feels a bit more predictable: Stephano maxes out his economy, bats away early incursions, and then stages an elegant last push. Grubby's as inventive as ever, but he could be giving in to the temptation to over-extend. Stephano puts him down.

The third game is a monster: it feels as long as the first two battles stuck together, and it ends with StarCraft at its grandstanding best: two massive armies, one made of frothing critters, another composed of glittering, spindly alien high technology, clashing and smashing together, pulling apart again, sneaking off to regroup, and then coming back for more.

This tie-breaker shows how confident Blizzard's game is when delivering a sustained kind of warfare - and how even long matches can be thrilling. The whole thing creeps towards the 50 minute mark according to the guy next to me, and it certainly feels like it. I'm a novice when I come to StarCraft multiplayer, but for this fight I'm there all the way as two guys build their armies and wait for a moment to turn a miniscule advantage into something a little more terminal.

Despite the intricacy of the designs, reading the landscape is never that difficult.

I can't fully grasp the depths, but I'm at least aware that they're in there, playing out in this case in a bravura set of tech switch-arounds that sees Grubby forcing Stephano onto the backfoot with each turn. Grubby's victory, while hard-fought, feels suitably emphatic. He's won the first semi-final. He's knocked out the apparent favourite. Even if that's it for him tonight, it's still a great story.

It's not the only story, of course: the other story's all about Heart of the Swarm itself, and how, even after a six month beta, it's primed to mix up the established multiplayer scene with its tweaks, its additions and its rebalances. That might shed some light on why the second round of games sees another upset with Spaniard Pedro "LucifroN" Moreno Durán , who I'm told was fairly widely expected to face Stephano in the final, defeated by Aleksey "White-Ra" Krupnyk, from the Ukraine.

The next day at Blizzard's European HQ, I chat to White-Ra about the fresh complexities that are emerging from Heart of the Swarm as he picks through the sort of questions - What's the scene like in your country? Do you worry you're getting on a bit? - that all celebrity sportsmen have to field. "It's changing things a lot," he says. "At first, old strategies almost didn't work for a while, and now the new units are bringing new abilities, new strategies. It's also good [at times like this]: when you use something you don't expect against an opponent you get an advantage, especially in the beginning. I'll use a surprise opening and try to destroy things quickly and that might work, and then I'll use a more traditional approach and lose."

Protoss architecture is a real pleasure to look at: you can tell a lot about their blend of strengths and weaknesses just by casting an eye over their buildings.

Making even minor tweaks to a game as popular as this can be dangerous, and that's something Blizzard's all too aware of. Lined up in the front row at Versailles are a group of developers: they're presumably enjoying the moment that their new game heads down the slipway, but they're also making mental notes, looking at unit match-ups and weighing potential patches. Sat down with David Kim, a balance designer on StarCraft 2 and also a leading Random player, I ask him about Blizzard's relationship with the community: about refining the build order that's brought them this far.

"It's everything together," says Kim. "In order to get such a moment, you not only need to create awesome units, but you need the community to back us up and also the pros to play the quality of games that they do play. Everything that goes into the game from our end has to work: we went through so many iterations of every unit that's in the game. The first idea we came up with for the Tempest, say, is not the Tempest we have now.

"This time around the design was much different in process," he continues. "Back with Wings of Liberty we didn't have the community available to us, so we focused on what's cool, what's fun. Now, we work heavily with the community and with the pro players throughout the six months of the beta. For us it's more important to make sure the unit belongs in StarCraft 2 rather than, 'If this is our idea we want it in a little more' versus 'if it's the community's we want it a little less.' It's not like that at all. We try to take that bias out as much as possible. With this kind of mindset you don't have to balance our ideas against their ideas, you just kind of think of it as a whole."

Throughout the Versailles matches I'm starting to get a glimpse of what balance really means for StarCraft 2 - how it's part of an on-going process. Making changes to an ecology as complex as this isn't about protecting a middle ground. It's about ensuring the whole thing never stops moving: incentivising new - or old and forgotten - builds, and allowing spaces for fresh tactics and strategies to blossom. It's there to keep the game alive, the way that infusions of weird portmanteaus and techy gibble-gabble keep the English language alive.

White-Ra, looking rather serious.

"Think about a match," concludes Kim. "Say it's Protoss and Terran: we want that match to be fair, but we want moments when, say, this player's a little stronger, then that player's a little stronger. That kind of repeats and it creates exciting games to watch: I want to attack right now because he's weak, and vice versa. Every game we're seeing between the four pros, everyone wants to be aggressive, no matter what match-up it is, and that's a much cooler idea of fairness than everyone having equal tools at every stage of the game."

Back on stage, it's almost as if Grubby's trying to make Kim proud. It's Protoss vs Protoss, and Grubby's first game against White-Ra is a masterpiece of aggression: with just one base built, he rushes the Ukrainian and the whole thing is over in minutes.

From there, the final two games pass in a blur: White-Ra takes the next one in a muddle of Void Ray fire - now those guys certainly look OP - and then Grubby clinches the conclusive battle in a match that's so wracked with tension I can't even bring myself to take notes. Also, my pen's rolled under a seat and my arms are quite short.

Grubby's done it! The underdog has won, and along with a nice little trophy, he gets to help wheel out an improbably large birthday cake for Stephano. Blizzard's big, but it never forgets the human touch, right? Since Stephano's a Zerg guy, the cake does not look particularly appetising - it's black, for one thing, and covered with complex ridges that suggest it might have gills - but no bother: there's half an hour until midnight in Paris, and Blizzard's minutes from opening the floodgates on a new game. Patchers around the world are primed to spark up, while firecrackers inside Versailles erupt to signal that a fresh worldwide battle is about to commence.

Ka-boom. For a few bright seconds, the stage is suddenly filled with streamers; the air is busy with twinkling glitter.