After a few opening minutes of back-and-forth play, Bayern quickly took advantage of Gabriel's aggressiveness. Robert Lewandowski's header, uncontested due to Gabriel zigging when he should have zagged, easily went past Petr Cech's left side, in the near post.
Arsenal thought they drew the match even just a couple minutes later, with Nacho Monreal's cross to Mesut Özil rocketing past Manuel Neuer. Bayern players, however, were quick to protest the manner in which Özil scored. It turned out that he shouldered the ball in, and the official quickly waved off the would-be tying goal on that account. Özil was given a yellow card for his efforts, on top of it.
Thomas Müller doubled their lead in the 29th minute with a strike from short distance, after a Kingsley Coman shot was deflected, fell neatly to left foot, and was comfortably dispatched past a diving Cech.
Before the half time whistle, Bayern went up three on Arsenal. David Alaba did sweet, delicious David Alaba things. deftly dribbling out of trouble in the face of attempted tackles and, with a couple of lovely first touches, sent a screamer from distance into the goal.
Some other stuff happened after the second half kickoff. Arjen Robben scored seconds after coming on for Coman, the ball was kicked around a bit more, fans cheered, Olivier Giroud scored a beauty off an Alexis Sanchez cross that was scissor-kicked after collecting and controlling it off his chest, flags waved, Douglas Costa hit the turbo button on a run through the middle and set free Lewandowski with a well-timed pass, who latched on, touched forward, and struck a low shot in for their fifth, and some other things.
Coupled with an Olympiacos win versus Dinamo Zagreb, Arsenal needs to win their last two matches, which includes a trip to Piraeus, and have Bayern absolutely clobber the Greek side in a few weeks, if they are to advance to the Knockout Rounds.