Bayern Munich spurned a host of chances as Leon Bailey's double earned 10-man Bayer Leverkusen a 2-1 win and inflicted a first defeat on Hansi Flick.
The champions had won each of their four matches without conceding since Flick was named interim boss following Niko Kovac's sacking, but they came unstuck in Saturday's Bundesliga clash at the Allianz Arena.
Thomas Muller scored his first goal in 21 league matches to cancel out Bailey's early opener, only for the Leverkusen winger to restore his side's advantage 115 seconds later.
Despite Jonathan Tah being dismissed nine minutes from time, a mixture of poor finishing and impressive goalkeeping from Lukas Hradecky left Bayern – who rattled the woodwork late on through Leon Goretzka and an unusually wasteful Robert Lewandowski – frustrated as they lost further ground in the title race.