Jurgen Klopp's side went ahead through Mats Hummels' fortuitous eighth-minute goal and missed the chance to double their advantage 10 minutes later when Nuri Sahin's penalty was saved by Christian Wetklo.

Dortmund argued Wetklo ought to have seen red for his foul on Lucas Barrios, which forced their top scorer out of the contest, and their anger was compounded when the Mainz keeper parried away Sahin's spot-kick.

The Mainz equaliser was also shrouded in controversy. The visitors played on despite Dortmund defender Neven Subotic lying injured and the move finally ended with Petar Sliskovic firing home.

Dortmund have been dominant in Germany this season but they are starting to wobble at a crucial time.

Last week's defeat at Hoffenheim gave the chasing pack hope and second-placed Bayer Leverkusen can increase the pressure on the Westfalians by beating Schalke tomorrow.

Hannover kept their bid for Champions League qualification on track with a 2-0 victory at home to Hoffenheim.

Didier Ya Konan gave the hosts the lead in the 38th minute and Mohammed Abdellaoue doubled the advantage in the 53rd minute.

Franck Ribery grabbed a late winner as Bayern Munich bounced back from their Champions League elimination to Inter Milan with a 2-1 win at Freiburg.

Mario Gomez put the Bavarians in front in the ninth minute, but Papiss Demba Cisse deservedly levelled for the hosts within 10 minutes, shortly after missing a penalty.

The home side looked capable of taking all three points until France playmaker Ribery crashed home a 25-yard drive in the 88th minute to save Bayern's blushes and keep them just two points behind Hannover.

Mladen Petric scored a hat-trick as Hamburg marked Michael Oenning's first match in charge with a 6-2 win over Cologne.

Petric scored the first to open the floodgates, with Anis Ben-Hatira making it 2-0 after 32 minutes.

Croatia international Petric struck again in the 38th and 43rd minutes as the hosts established a 4-0 half-time lead.

Mato Jajalo cut the deficit to 4-1 in the 50th minute before Gojko Kacar pushed the lead to 5-1 shortly after.

Ze Roberto scored a final time for Hamburg from the spot in the 58th minute before Lukas Podolski grabbed a consolation.

Theofanis Gekas scored twice as Eintracht Frankfurt beat St Pauli 2-1 to end a nine-match winless run.

Gekas converted a penalty in the 34th minute to give Frankfurt the lead before Charles Takyi levelled the scores approaching half-time.

Gekas struck again in the 77th minute for the winner.

Sandro Wagner scored two penalties as Werder Bremen ended 10-man Nurnberg's eight-game unbeaten run and took a big step towards avoiding relegation.

Wagner gave Bremen the lead in the 27th minute before Ilkay Gundogan equalised on the half-hour mark.

Claudio Pizarro made it 2-1 for Bremen five minutes into the second half and the hosts' prospects looked even brighter when Nurnberg's Timothy Chandler received a second yellow card with 18 minutes to go.

Wagner's second spot-kick of the afternoon sealed the win to move Bremen up to 12th, while Nurnberg remain in sixth.