Although the match began at least somewhat promisingly for Arsenal, who managed to give the visitors a bit of a scare when Theo Walcott burst down the left wing and earned a corner kick which error-prone goalkeeper Manuel Neuer made a mess of. And then... well, things went downhill.
Bayern Munich possess an astonishing array of attacking talent, but perhaps the most impressive is 23-year-old Toni Kroos. And it was Kroos who opened the scoring seven minutes in, when the visitors overloaded the right side to allow Thomas Müller to send a cross to the top of the box. Aaron Ramsey lunged for a block but couldn't reach it, and Kroos met the delivery with a lovely 20-yard effort which bounced off the Emirates turf and buried itself in the back of Wojciech Szczesny's net.
The visitors weren't done there, and Arsenal made life difficult for themselves by giving away free kicks in dangerous positions. Daniel van Buyten saw his overly elaborate free kick routine fail to come off but managed to earn his side a corner anyway thanks to some odd defending, while Bastian Schweinsteiger's effort, earned after an awful Per Mertesacker giveaway, was deflected behind for a goalkick.
With Arsenal notoriously vulnerable on set pieces, it seemed like only a matter of time before their rearguard was breached once more. Bayern produced an opening via the somewhat strange method of punting long to Javi Martínez, who beat the offside trap and forced Laurent Koscielny to concede a corner. And from said corner, the visitors went 2-0.
Szczesny was at least partially to blame. Van Buyten's near-post header was hit hard but right at the 22-year-old keeper, and although Szczesny managed to stop the shot he failed to keep it out of the danger zone, virtually dropping it on Müller's toes. The surprised, off-balance midfielder reacted quickly, prodding the loose ball into the roof of the net for a second away goal.
A visibly frustrated Arsenal side took out their rage on Bayern's players. Bacary Sagna went into the book for a nasty foul on Kroos, and he was soon joined by Mikel Arteta as the former Everton man scythed down Mario Mandzukic on the Gunners' left.
There were some faint signs of hope, however. Mertesacker had a shot blocked, as did Theo Walcott a few minutes later, and there was good news when Schweinsteiger picked up a booking that will rule him out of the next leg for a foul on Ramsey, although a cynic might suspect he was deliberately picking up the card to reset his count. And the halftime score could have been worse -- Mandzukic should have put the visitors 3-0 up when he met Philipp Lahm's excellent delivery only to nod just wide of the post.
The Gunners began the second half with plenty of intent, and they managed to get back into the game thanks to a bizarre Lukas Podolski goal which saw the Germany international win a corner kick by deflecting Santi Cazorla's shot wide and nod home the set piece when Neuer opted to run around in circles underneath it for no reason after calling his own defenders off.
Bayern looked fairly confused at having conceded, but the goal seemed to further invigorate Arsenal and it no longer seemed wholly out of the question that they could get something out of the tie. But the visitors were still incredibly dangerous, and Szczesny was forced to save well from Kroos before Martínez hit a free header just over.
Arjen Robben was then thrown into the fray by Jupp Heynckes, and his first action saw him drift offside when it looked like Kroos would find him clean through on goal. His second was to force Podolski into a foul, one that earned the goalscorer a booking, and Ramsey got one as well when he hacked down Müller on the edge of the box. Fortunately for the Welshman, Schweinsteiger's subsequent effort was hit well high.
Arsenal were getting half-chances too, with the impressive Jack Wilshere and Podolski getting chances to drive into the box only for the former to lose control and the latter to shoot well wide. Then came the big opportunity. Tomas Rosicky sprayed a clever ball out wide, and Walcott's cross was met by substitute Olivier Giroud in the centre. The excellent work, however, was ruined by his shot, which was hit hard but straight at Neuer -- the goalkeeper wouldn't have been able to keep that shot out even if he'd wanted to.
And then Bayern struck again. Robben managed to get himself isolated in the centre against erstwhile left back Thomas Vermaelen, and the winger was able to find Lahm on the overlap. The subsequent cross was met by some tangle of Mandzukic and Sagna at the back post, and the ball looped over a helpless Szczesny and dropped into the back of the net in what seemed like slow motion.
Down 3-1, Arsenal didn't give up. Wilshere immediately drew another save out of Neuer, although like Giroud before him he directed his vicious effort straight at the goalkeeper when he should have done better. But the visitors were clearly the better side, and Mario Gomez very nearly made it four when his deflection forced a flying save from Szczesny before the striker blasted the rebound high and wide.
It seems unlikely that Bayern will regret Gomez's miss. After an uneventful three minutes of injury time, the Germans came away from the Emirates with an emphatic and thoroughly deserved win. Up by two with three away goals, they're all but through to the quarterfinals.