Champions Bayern Munich suffered a 3-1 loss at Mainz 05 on Saturday following a toothless appearance, only a week after the high of clinching their 10th straight Bundesliga crown.
Mainz outclassed the visitors throughout the game and hit the woodwork twice in the opening 11 minutes.
They could have scored several more goals, with Bayern in no mood to put up a real fight after winning their only silverware of the season last week.
Bayern coach Julian Nagelsmann had promised "maximum seriousness" ahead of the game but instead saw his players lack any spark or urgency even after a strong start by Mainz.
"It was not something I enjoyed. Mainz did it well. They had many chances and deserved to win. They had good energy and we did not have it," Nagelsmann told reporters.
"After the 10th straight league title it can happen, it's human. But still the passion should be visible, the effort to not let in goals. Mainz could have scored eight or nine goals."
"We have had a few games this season where opponents had many chances," said Nagelsmann, in his first season at Bayern.
Mainz took the lead with Jonathan Burkardt's missile from 14 metres in the 18th minute.
The hosts, who had 24 efforts on goal compared to Bayern's four, scored again when Moussa Niakhate stabbed the ball in at the far post from a corner.
Bayern had to wait half an hour for their first good chance when Eric Maxim Choupo-Moting hit the woodwork.
They did pull a goal back with Bundesliga top scorer Robert Lewandowski bagging a league record 18th away goal of the season and his 34th league goal this term.
But just as Bayern piled on the pressure after the break Mainz struck again thanks to a textbook break as Leandro Barreiro's shot took a deflection in the 57th to restore their two-goal cushion.
Bayern have 75 points from 32 games, 12 clear of second-placed Borussia Dortmund, while ninth-placed Mainz have 42 with two rounds of matches left.
