HAMBURG (REUTERS) - Robert Lewandowski struck twice as champions Bayern Munich won 2-1 at Hamburg on Friday to stretch their lead at the top to 11 points, as the German Bundesliga resumed following a one-month winter break.

The Bavarians made a slow and sluggish start before the Poland forward put them in front with a 37th-minute penalty.

Hamburg remained disciplined at the back and got their reward eight minutes into the second half, when Xabi Alonso put through his own net.

Lewandowski restored Bayern's lead in the 61st minute, deflecting a Thomas Mueller shot and wrong-footing keeper Rene Adler to take his Bundesliga goal tally for the season to 17, one behind Borussia Dortmund's Pierre-Emerick Aubameyang.

David Alaba then hit the post with a superb free kick as Pep Guardiola's Bayern carved out more scoring chances.

Spaniard Guardiola, who leaves at the end of the season and has said he will be joining an English Premier League club, is chasing his third straight domestic title, while the Bavarians are on track for a record fourth consecutive Bundesliga crown.

Bayern have 49 points from 18 games. Dortmund, in second place on 38, travel to Borussia Moenchengladbach on Saturday.