Liverpool suffered a shock 2-0 defeat to Atalanta on Wednesday.
Jurgen Klopp fielded a much-changed side to the one that beat Leicester City on Sunday.
And it backfired for the German as Atalanta a victory which will be celebrated widely in Bergamo.
Second-half goals from Josip Ilicic and Robin Gosens were enough for Gian Piero Gasperini's to take all three points.
The loss means Liverpool will have to wait to book their spot in the knockout rounds, but they still sit on top of Group D.
Speaking after the game, Jurgen Klopp admitted his side were not at their best.
He said: "It was not a good game. Both teams didn't create a lot, until they scored the goals.
"A deserved defeat in a difficult game. The referee didn't whistle a lot and that makes it even more difficult, for both sides. It was unbelievably intense and you need some breaks.
"When the first half is gone, you usually settle - but for some players who didn't play for a while it was very intense for them. We didn't find a way in the game.
"We had moments but not real chances. It could happen to other teams. You ask us to go Saturday at 12:30, which is nearly a crime. That is nothing to do with the result, but congratulations to you.
"Thumbs up, no injuries and we go again."