Paco Alcacer scored the winner as Bundesliga leaders Borussia Dortmund twice came from behind to beat defending champions Bayern Munich 3-2 and move seven points clear of their third-placed rivals.
The result on Saturday piles added pressure on Bayern head coach Niko Kovac, as his side's chances of winning a seventh straight title in his first season in charge took another blow.
"We allowed ourselves to be beaten twice on the counter, that shouldn't have happened," said Kovac.
"We should have been more compact and unfortunately we lost a game which should have been a draw," he added after Robert Lewandowski had two second-half goals disallowed for offside.
Bayern have now been beaten in three of their last six Bundesliga games after defeats by Hertha Berlin and Borussia Moenchengladbach, managing just eight points from the last 21 available.
They will drop to fourth in the table on Sunday if RB Leipzig beat Bayer Leverkusen at home.
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Lucien Favre's Dortmund remain unbeaten and four points clear of second-placed Gladbach at the top of the table.
After Lewandowski twice gave Bayern the lead at Signal Iduna Park against his former club, Dortmund captain Marco Reus hit two equalisers before substitute Alcacer struck in the 73rd minute.
"We didn't trust ourselves in the first half, but we played awesome football after the break and it was great fun," said Reus.
Alcacer has now scored eight goals in six league appearances since signing on loan from Barcelona.
Bayern took a deserved lead when Serge Gnabry curled in a cross for Lewandowski to power a header past stand-in Dortmund goalkeeper Marwin Hitz on 26 minutes.
It was 1-0 at the break, but Dortmund drew level when Manuel Neuer brought Reus down in the area in the 49th minute and the skipper calmly converted the penalty.
Lewandowski restored the lead three minutes later, heading home his second -- his 14th goal in 16 matches for Bayern against Dortmund, who he left in 2014 on a free transfer.
Reus had a chance cleared off the line on 59 minutes, just before Lewandowski had the ball in the Dortmund net, but was flagged for offside.
- Tense finish -
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- Plea hat-trick -
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