Substitute Ji Dong-won made the most of a counter-attack as too many men in blue stood and watched, and the chance to establish a gap over rivals Manchester United evaporated.
Asked if that was good enough, Mancini replied: "No, not for a top team. In that situation, we attacked with eight players and the same players who attack need to come back and run quickly.
"I know football and for that reason in the last 15 minutes, I continued to call [central defenders] Vinny [Vincent Kompany] and [Joleon] Lescott to say, 'Stay there, stay there, don't leave the space', because that was dangerous.
"We continued to attack and sometimes we wanted to attack with 10 players. This is impossible.
"But that's it, it's finished. We have a game in 48 hours and we need to recover now."