Eren Derdiyok hugs Kiessling after Leverkusen's equaliser [AFP]

The league's leading scorer Stefan Kiessling took his league tally to nine this season when he levelled on 14 minutes after Bayern had taken an early lead through striker Mario Gomez.

Undefeated Leverkusen have 27 points from 13 matches, one ahead of Werder Bremen who demolished Freiburg 6-0 on Saturday.

Bayern, who have now drawn for the third consecutive match and have won only two of their last seven league games, are in seventh place on 21 points.

Hamburg could also move up to 26 points with a win against lowly VfL Bochum later on Sunday.

Coach Louis van Gaal, under mounting pressure given Bayern's mediocre season so far, gave a rare starting spot to Gomez and the German international quickly justified his selection.

A defensive blunder allowed Miroslav Klose to send Gomez into the box to slot home after eight minutes as Rene Adler rushed out of his goal.

The celebrations among the majority of the 69,000 fans did not last long.

Kiessling chased down a long ball from Arturo Vidal, comfortably shook off defender Daniel van Buyten and fired past keeper Hans-Joerg Butt.

The gifted striker was a constant threat and repeatedly left his markers standing, exposing Bayern's chronic problem in central defence since the departure of Brazilian Lucio in the close season.

Bayern's defensive midfielder Anatoliy Tymoshchuk should have done better a minute before the break when he was left unmarked in the box but only managed a weak shot that Adler had no trouble blocking.

Adler then made the save of the match with five minutes left when he denied Gomez from close range.