Arjen Robben fired Bayern ahead in the 11th minute with a trademark goal, cutting inside to his stronger left foot before firing an unstoppable shot past a helpless David Ospina in the Arsenal goal.

But Arsenal fought back gamely and Alexis Sanchez equalised on the half-hour, finally managing to force home a rebound from a penalty at the third attempt after Robert Lewandowski fouled Laurent Koscielny in the area.

Only fine saves from Manuel Neuer to deny Granit Xhaka and Mesut Ozil prevented the Gunners from taking a half-time lead.

However, Arsenal visibly wilted after losing captain Koscielny through injury on 49 minutes. Bayern proceeded to take full advantage of his absence, firing three goals in a breathtaking 10-minute spell courtesy of Lewandowski and a Thiago brace.

Substitute Thomas Muller applied the finishing touches to a resounding 5-1 win to seal the 16th consecutive Champions League win on home soil for Bayern.

"We played fantastic football with good intensity and balance," Ancelotti said at the postmatch news conference. "We started well but Arsenal equalised and we had problems at the end of the first half. But during the second half the spirit was good."

Ancelotti reserved special praise for two-goal hero Thiago: "He played really well and also managed to score twice. It was a perfect performance.

"The result is really important, we have the advantage,"

Ancelotti then warned against complacency ahead of the second leg in the English capital next month, adding "this is only one game."

"We have to prepare well for the game in London. We want to avoid problems so we have make sure we play with the same intensity, spirit and concentration."

And Ancelotti praised sub Muller for adding the finishing touches to the scoreline with a goal two minutes from time.

"I'm really happy for him. He scored a fantastic goal, he deserved this and he looks forward to the future with optimism. I'm sure he will be vitally important for us in the future."

Captain Philipp Lahm, who is retiring at the end of the season, admitted his team flagged after conceding the penalty and were happy to make it into the dressing room on level terms.

"But we were sensational after," said the retired Germany international.