Watch: Bayern pulls away from Arsenal through Thiago, Lewandowski

Arsenal has high hopes of getting over the Champions League round-of-16 hump for the first time since 2010, but it's looking more likely that for a third time since 2012-13, the Gunners will be ousted by Bayern Munich.

A dominant second half from Bayern Munich resulted in a 5-1 thrashing in the first leg, putting Arsenal in a massive hole heading back to London. Robert Lewandowski and Thiago Alcantara combined for three goals in a 10-minute span, and Thomas Muller put the finishing touches on the rout with a goal off the bench late.

Arsene Wenger's side entered this stage as a group winner, while Bayern was a runner-up to Atletico Madrid in the group stage. That didn't matter in the early going at the Allianz Arena, where Arjen Robben curled a left-footed blast by goalkeeper David Ospina to give Bayern a 1-0 lead in the 11th minute.

Arsenal found an equalizer at the half-hour mark, with Alexis Sanchez scoring a valuable away goal. It came after Lewandowski was whistled for the penalty after his inadvertent kick of Laurent Koscielny, which sent Alexis to the PK spot. Manuel Neuer saved his spot kick, but Alexis persevered and followed up on a second rebound, making it 1-1.

After Koscielny was forced off through injury, Bayern re-took the lead in the 53rd minute through Lewandowski, who completed a well-timed run with a clinical finish from inside the box.

That lead quickly became 4-1 after Thiago scored twice against a reeling opponent, with the first coming off a first-class set-up from Lewandowski and the second a long-range volley that nutmegged a defender before wrong-footing Ospina. 

As if that wasn't enough, Muller got in on the act just before the final whistle. Replacing Robben, Muller, who has struggled to find his top form this season, finished low into the corner, making it 5-1 and making Arsenal's second-leg task that much more difficult and elimination at this stage that much more likely.