Bayern Munich opened the second half of the Bundesliga season with a 2-1 win at Hamburg on Friday as Robert Lewandowski's goals took Pep Guardiola's side 11 points clear.

Bayern's march to an historic fourth German league title seems unstoppable as Guardiola, who has said he will leave in May, attempts to sign off his three years as coach with the treble of Champions League, German Cup and Bundesliga titles.

With second-placed Borussia Dortmund at resurgent Borussia Moenchgladbach on Saturday, Bayern took their chance to extend their lead at the top of the table as the league resumed after the four-week winter break.

Poland striker Lewandowski's goals took his league tally to 17 this season and 25 in all competitions.

Bayern took the lead in sub-zero temperatures at Hamburg's Volksparkstadion when referee Felix Zwayer judged Thomas Mueller had been fouled by Hamburg goalkeeper Rene Adler just inside the area when they both went for the ball.

The decision looked harsh and Adler was shown a yellow card, but Lewandowski stepped up and drilled home his 24th goal in 28 games this season on 37 minutes.

It was not what Hamburg deserved for their battling display, but the hosts pulled themselves level at the start of the second half.

Veteran midfielder Aaron Hunt launched a towering free-kick which both Bayern's Xabi Alonso and Hamburg's Pierre-Michel Lasogga failed to connect with and the ball bounced over Manuel Neuer into the Munich net on 53 minutes.

Things went from bad to worse for Bayern as Germany centre-back Jerome Boateng called to be replaced after appearing to injure his right groin in a tackle.

But the scores were level for just eight minutes as Mueller drove home a Javi Alonso cross, Lewandowski stood in the ball's flight path and stabbed it home from close range from a position which was right on the offside line with an hour gone.

His second goal of the game left him with 17 goals in 17 German league games this season, but still one short of Borussia Dortmund's Gabon forward Pierre-Emerick Aubameyang.

Bayern could have grabbed a third when David Alaba's free-kick clattered the crossbar with Adler well beaten and only a superb save denied Thiago Alcantara's shot.

This was Bayern's 70th victory in 87 Bundesliga games under Guardiola and means they are unbeaten in their last 13 league games against Hamburg, dating back to September 2009.

But Bruno Labbadia's side, who remain 10th in the table, can take heart from an impressive display and they played far better than in their recent 5-0 and 8-0 drubbings at the hands of Bayern.