By Richard Clarke in Barcelona
Arsenal are out of the Champions League. Their challenge foundered at the feet of one man - Lionel Messi.
After Nicklas Bendtner's breakway gave the visitors an unlikely lead in the 18th minute, the little Argentinean artist took control. He whipped in the equaliser three minutes later, swept home a second eight minutes from half time and, best of all, impishly chipped Almunia just before the whistle.
It was a mesmeric hat-trick inside 19 minutes and killed off any chance of progression for Arsène Wenger's team.
Barcelona kept their counsel in the second half. Pep Guardiola shackled his side for the sake of qualification.
Messi fired home a fourth in the dying minutes just to make sure. It meant this memorable tie would not go out with a whimper when it had started with such a bang.
Barcelona's progression is richly deserved, they were the by far the better side over the two legs. But Arsenal pushed them hard during an enthralling 180 minutes.
That two-goal comeback at Emirates Stadium and one-goal lead at Nou Camp says much about Wenger's fledglings.
This second leg might been more interesting had the visitors been blessed with a few less injuries.
Arsenal were beaten tonight and beaten well.
But it is never a disgrace to beaten by the best.
Wenger's team-sheet made difficult reading pre-match. In the first leg he had lost three key players - Cesc Fabregas (broken leg), Andrey Arshavin (calf) and Willam Gallas (calf). Another Alex Song (cartilage) did not make it past the 1-0 victory over Wolves last weekend.
And, most crucially of all, one of the replacements, Sol Campbell, failed a late fitness test on his strained hamstring. At least his deputy Mikael Silvestre had experience at the highest level. Because that was where Arsenal were playing this evening.
Perhaps the absence of Campbell led to the selection of Theo Walcott, perhaps Wenger was going to do it anyway. But it certainly gave the visiting XI as attacking feel. As expected Abou Diaby and Bendtner returned the team.
Barcelona had their share of problems too. No Carlos Puyol, no Gerard Pique, no Zlatan Ibrahimovic. Gabriel Milito and Rafeal Marquez came in at centre back, Bojan Krkic replaced the Swedish striker. As in North London, Thierry Henry was left on the bench.
This was what Champions League football was all about. A magnificent stadium, two great footballing sides, both with realistic ambitions of going through...
... and lots and lot of pressure.
However in contrast to the game at the Emirates Stadium, this encounter started sedately. Yes the opening quarter was all Barcelona but they only conjured a couple of chances and, worringly for Arsenal, Messi was the magician.
His curling cross-shot forced Almunia to stretch his frame and fingertip the ball wide. Then in the 11th minute, he pounced on Gael Clichy's weak clearance and whipped a shot over the angle of post and bar. It rippled the roof of the net on route. If Messi was on the money this evening - the visitors were in trouble.
You really could not see an Arsenal goal. Although they been solid so far, they had not done much going forward.
And then they scored.
In the 18th minute, Diaby thieved the ball in midfield and, with Barcelona horribly overstretched at the back, fed Walcott on the right. He had acres of space to run into and, within seconds, was baring down on keeper Victor Valdes.
The England winger elected to square the ball to onrushing Bendtner. Under pressure from Daniel Alves he could only stumble a shot at Valdes. But the rebound fell kindly and the Dane recovered quickly to stab the ball home.
It was everything Arsenal needed. It gave them momentum, hope and, of course, the lead in the tie.
The feeling lasted less than three minutes.
Messi ran in from the right, straight at the visitors' defence. He lost control but Silvestre's touch acted as a one-two. The Argentinean shrugged off Denilson and crashed a shot into the top right hand corner from just outside the area. A quality strike.
The exchange of goals stoked up a game that needed no more heat.
A Daniel Alves free kick forced an uncomfortable save from Almunia after Denilson had been booked for foul on Messi. A couple of minutes later the striker cut in from the right and teased Silvestre before sending a rasping drive into the sidenetting.
The little maestro had been quiet in London. This evening he was at the hub of everything. It was no surprise, when eight minutes from half time, he scored again.
Sergei Busquets' pass allowed full back Eric Abidal to get behind the Arsenal defence on the left side and he crossed low into the area. Silvestre's stabbed clearance was touched back by Pedro Rodriguez for the scampering Messi. His first touch took him beyond Clichy, his second rammed the ball home.
Arsenal were already suffering at the feet of a master. Five minutes later, he twisted the knife. Abidal's header caught the visiting defence napping and Messi burst through to complete his hat-trick with an cheeky shovel shot over Almunia.
The first half had been a exquisite exhibition of football by Messi and it was little wonder that, when it ended, the cavernous Nou Camp resounded with chants of his name.
Arsenal seemed to be in the impossible position of having to attack a side who seemed fully capable of picking them off.
But they did their best to impose themselves and Guardiola's concern was clear when he replaced striker Krkic with Yaya Toure, a defensive midfielder, 10 minutes after the restart.
The Barcelona coach was not settling. He was sitting and waiting for Arsenal. Wenger's men did come forward but in a considered, cautious way. It was entirely understandable.
On the hour Diaby's pass found Bendtner momentarily on the penalty spot but Marquez timed his challenge perfectly.
Arsenal were forcing themselves on Barcelona a bit more but not enough to prise an opening.
Wenger replaced Silvestre with Eboue and moved Sagna into central defence alongside Thomas Vermaelen. But by now Barcelona were withdrawn. Their commitment to going forward had flagged for the first time in the tie.
Diaby's raking cross-ball found Rosicky at far post but his first-time shot flew horribly high. Barcelona might have extinguished any hope when Messi's quick free-kick caught out the Arsenal defence and Pedro's lob drifted just wide.
Just before Eduardo replaced the tiring Rosicky, Bendtner headed the ball against the post. However he had been flagged offside. Fifteen minutes from time, Clichy strode forward and cracked a shot over the bar when he should have opted for Eduardo on the left.
The noise at the Nou Camp grew as the minutes ticked away. Barcelona were seeing off the game with composure, Arsenal seemed spent.
When Maxwell tested Almunia at the near post it was the home side's first real chance of the half.
But you almost knew Messi would have one last occasion.
It arrived in the 88th minute.
With Arsenal undermanned at the back, he weaved through Eboue and Vermaelen only to see his first shot beaten away.
His second went through the keeper's legs.
Messi 4 Arsenal 1.
- Almunia (C)
- Silvestre 64
- Denilson Yellow Card
- Rosicky 74
- Bendtner Goal!
- Eboue 64 Yellow Card
- Eduardo 74
- Dani Alves
- Abidal 53
- Bojan 55
- Messi Goal! Goal! Goal! Goal!
- Maxwell 53
- Yaya Toure 55