German Cup holders Bayern Munich lost to lowly second-tier side, Holstein Keil 6-5 on penalties to crash out of the competition.
The regulation time ended 2-2 before the modest club stunned the treble winners.
Both teams score their five spot-kicks, Bayern’s Marc Roca had his effort saved then Fin Bartels scored the winning penalty for Holstein Keil to claim a memorable victory.
“We lost to the underdogs Kiel and they did everything they could,” Mueller said. “We had chances in the first half. But we made mistakes and Kiel punished us.
“They were very efficient but we should have won the game. We are out and it is bitter. It is difficult to say we did not invest everything. That’s positive but it is frustrating to be eliminated.”
“We believed throughout that we could make the spring a big surprise here tonight,” Bartels said. “We said we will make all our penalties and we did. But overall I think it capped a very good performance from us and we deserved it.”