Arjen Robben felt Bayern Munich were sleeping before being roused to inflict a devastating Champions League humiliation upon Arsenal.

Bayern ran out 5-1 winners in the first leg of the last-16 tie at the Allianz Arena last month and, despite falling behind to a blistering Theo Walcott strike in the first half, they repeated the feat after Laurent Koscielny was sent off for a foul on Robert Lewandowski.

The Poland striker converted the resulting spot-kick and Robben gave Bayern the lead on the night before substitute Douglas Costa got in on the act and Arturo Vidal added a late brace.

It meant Bayern dealt out the heaviest defeat suffered by an English team in Champions League history but Robben was far from satisfied with how they went about their business during the first half.

"The first half was not good," he told BT Sport. "We spoke about it before the game. We knew what was going to happen - they were going to push

"But we were sleeping. For second balls we were not there. In the quarter-finals we have to improve

"The second half was much better and the penalty and the red card helped.

"They played aggressive in the first half. They created some danger and some chances and had an opportunity for the second goal.

"The penalty and the sending off changes the game but I think it was a clear penalty and, if you are the last man, it is a sending off."

Bayern lead the way in the Bundesliga and are into the semi-finals of the DFB-Pokal, although Robben is not keen to talk about European glory and a possible repeat of their 2013 treble just yet.

"We have to go step by step. I don't like to talk about finals," he added.

"If you see all the teams going through to the quarter finals, it is already going to be a very hard one.

"As I said, step by step and both feet on the ground."