Visitors Schalke put a dent in Bayern Munich's Bundesliga title hopes by snatching a 1-0 win over the champions in a bad-tempered game on Saturday.
Schalke's victory left Bayern down in third place and in danger of falling six points behind leaders VfL Wolfsburg with just five games left to play.
It also left under-fire coach Juergen Klinsmann in an uncomfortable position, after thousands more joined the "Klinsmann out" chants at the Allianz Arena on Saturday following yet another mediocre performance.
Bayern have never gone top this season.
"This is an extremely bitter defeat for us," Klinsmann said. "We expected a lot and started well but we lost our rhythm after the goal."
"I accept the criticism against me but the work with the team is still going well and is a lot of fun," he said.
Schalke's Halil Altintop grabbed the winner in the first half before each side had a player sent off with a second booking, Schalke's Jermaine Jones for a foul on Mark van Bommel and Franck Ribery for shoving Jefferson Farfan.
Wolfsburg, who play second-from-bottom Energie Cottbus on Sunday, lead on 57 points, with Hertha Berlin second on 55, after beating Hoffenheim 1-0 on Friday.
Bayern are third on 54, ahead of VfB Stuttgart and Hamburg SV on goal difference.
Stuttgart beat Eintracht Frankfurt 2-0 with goals from Cacau and Mario Gomez, while Hamburg slumped to a 2-0 defeat against Borussia Dortmund.
Schalke made a great start and deservedly grabbed the lead through Halil Altintop when he snuck into the box to head home a Christian Pander corner midway through the first half.
The visitors, who have now won all four matches under an interim coaching trio of Mike Buskens, Youri Mulder and Oliver Reck, could have doubled the lead through Farfan but the Peruvian striker's close range shot flew wide.
Bayern yet again lacked creativity, although they did come close when Jose Sosa whipped a free kick against the bar in the 37th minute.
Tempers boiled over in the second half when Jones was booked for a second time for a foul on Bayern captain van Bommel, leaving Schalke down to 10 men with 20 minutes to play.
Bayern restored the balance six minutes later when Ribery was sent packing with a second yellow card for shoving Farfan.
Schalke's lone striker Kevin Kuranyi came close to a second goal from three metres after Bayern keeper Joerg Butt palmed away a low Pander drive but hit defender Martin Demichelis.
"The team can be proud today," Buskens said after Schalke's first win in Munich since 2004. "We invested a lot and we were rewarded."