Bayern Munich's director of sport Matthias Sammer has accused the European champions of a lacklustre display in their 2-0 win over Hanover ahead of their opening Champions League match.

"We play football without emotion, we're just going through the motions, we have to get out of this comfort zone," fumed Sammer after the win in Munich left Bayern second in the Bundesliga.

Bayern start their Champions League campaign at home to CSKA Moscow on Tuesday and Sammer described the Bavarian giants as going into their "full-throttle week" with the handbrake on.

Sammer said any talk of readjustments under new coach Pep Guardiola was just "alibi rubbish" and insisted Bayern's stars should not have needed a passionate pre-match speech by Guardiola.

"It's all Pep this, Pep that -- it's not his fault, but it makes everyone else a little less responsible around here," said Sammer.

"Everyone wants to play well, that's without question, but the coach had to give a fiery speech before we really get going."

Sammer pointed to rivals Borussia Dortmund having secured top spot with a 6-2 romp over Hamburg.

"We are at the same point in the season where Dortmund gave everything away last year," said Sammer, while Bayern chairman Karl-Heinz Rummenigge described Dortmund's victory as a "warning".

Guardiola admitted Bayern had struggled to find their rhythm after the bulk of his squad only returned from international duty on Wednesday with several of their stars injured.

Second-half goals by Croatia striker Mario Mandzukic and France's Franck Ribery settled the win.

"We didn't do well in the first-half," said Ribery, as Bayern enjoyed around 70 percent ball possession.

"It is always difficult after an international break, we had more power in the second half, when we scored the goals.

"The main thing is we got a win, which was important."

But Dortmund's flawless record leaves Jurgen Klopp's team top of the Bundesliga ahead of their Champions League trip to Napoli on Wednesday.

"That was simply awesome, it was fun just to watch," said Klopp.

"Towards the end, my heart was singing and apart from the two goals we conceded, we defended well."

New signing Pierre-Emerick Aubameyang netted twice, as did Poland striker Robert Lewandowski, as Champions League runners-up Dortmund pulled away after Hamburg had levelled at 2-2.

Dortmund produced some superb second-half football including a sublime pass from Germany winger Marco Reus to Lewandowski for the fourth goal.

"When you get one of those through, then you're in heaven," said Klopp referring to the audacious pass.