Eintracht Frankfurt crushed 10-man Bayern Munich 5-1 on Saturday to send them tumbling to fourth in the Bundesliga, four points behind leaders Borussia Moenchengladbach who won 2-1 at Bayer Leverkusen.
The Bavarians, who have clinched the last seven league titles, have now won just one of their last four Bundesliga matches.
Saturday's heavy defeat on Thomas Mueller's 500th game in all competitions for Bayern leaves the future of embattled coach Niko Kovac in doubt.
First-half goals from Filip Kostic and Djibril Sow put the hosts in the driving seat with Bayern down to 10 after the ninth minute dismissal of Jerome Boateng with a red card for a foul.
The Bavarians briefly cut the deficit in the 37th minute through Bundesliga top scorer Robert Lewandowski, who has now netted at least once in each of their 10 league games.
The Poland striker took his league tally to 16 goals but David Abraham restored Frankfurt's two-goal cushion in the 49th.
Martin Hinteregger's header on the hour made sure of the three points and Goncalo Paciencia completed a horrible afternoon for Bayern, piling more pressure on the champions ahead of next week's big clash with Borussia Dortmund.
Gladbach, on 22 points, increased their lead at the top to three over Dortmund, who beat Vfl Wolfsburg 3-0 to snap their unbeaten run in the league and move into second place.
Marcus Thuram got the winner for clinical Gladbach after Kevin Volland cancelled out Oscar Wendt's lead for the Foals with all the goals coming in the first half.
RB Leipzig demolished Mainz 05 8-0 to go third on 18, ahead of Bayern on goal difference.
