Pep Guardiola celebrated taking charge of Manchester City for the 100th time in the Champions League on Tuesday, but it was Bayer Leverkusen and their fans that were left dancing at full-time.
The Bundesliga side would have been expecting a tough evening upon their delayed arrival in England, but it turned into a memorable 2-0 victory to leave Guardiola stunned on his milestone moment.
The Spaniard said in Monday's pre-match news conference that there had been "more disappointments than good moments" for himself and City in Europe's elite club competition and this was another of those lows.
The defeat was self-inflicted - Guardiola gambled with his starting line-up by making 10 changes to the side that lost at Newcastle on Saturday and the decision backfired in spectacular fashion.
"I have to accept it," Guardiola told TNT Sport of any criticism to the number of changes. "If we win it wouldn't be a problem so I have to accept it that maybe it's a lot."
The Spaniard added: "I always had the belief of the long season and everyone had to be involved but maybe it was too much. They played not to make mistakes instead of doing what we had to do.
"It was not the performance that we thought. I take full responsibility. We missed something. We missed an incredible opportunity and now we need to fight in the next games."
Leverkusen boss Kasper Hjulmand said of City's line-up: "It is a very tight programme for all teams. The normal rotation (number of changes) for a Champions League team is 5.5 players but no matter who they put on the pitch is a quality team."