The Blues came from a goal behind to level via a David Silva deflection midway through the second half, but were undone by a spectacular late Wayne Rooney winner that Mancini accepts no team in the world could have prevented.
“We were beaten by a moment of genius and I think that this was the only way we were going to lose this match,” said Mancini.
“I thought we were in control for large parts of the match and after we levelled, I thought we would go on to win the game or draw at the very least.
“I think we played very well and I’m very proud of my players, but sometimes football can be cruel and they scored a fantastic goal that we could do nothing about.”
Mancini believes the Blues will find it hard to catch United in the remaining months of the campaign, but says the title race is far from over- and he is also hoping for a change of luck in future top four battles.
“It will be difficult for us to catch United because we are now eight points behind them again, but will try our best and continue,” he said.
“We lost this game but didn’t deserve to – maybe the next time we play an important game we won’t play as well as we did today, but end up winning.”
