The Blues’ boss also said his team had done enough not only to have earned a point after a magnificent second-half fight-back, but perhaps should have gone on and won the game in the time that remained.
“It’s very hard to lose a derby, but even more so in the last minute so I’m very disappointed,” said Mancini. “We dominated the second-half and for this reason, I am really disappointed.
“They scored from their first two goal-scoring opportunities but after that, we dominated the game and fought back really well, but we can’t then give a goal away after working so hard.
“I think we made a mistake for the Van Persie free-kick at the end by only putting three men in the wall. I wanted four but I couldn’t get the instruction over and I think that cost us the goal.
“We should have defended this free-kick better and we had chances to win this game, but there is nothing we can do about it now.”
Mancini also claimed he didn’t want Mario Balotelli, who was withdrawn shortly after the second-half started, to waste his talent.
“Mario didn’t do what we wanted him to do today, but he has incredible ability and I love him as a person and a player, but he needs to produce that talent during games.
“He is young and has talent and I thought he could cause United a lot of problems. I don’t want him to waste all the talent he has.”
Mancini remained upbeat despite the Blues’ first league defeat of the season, adding: “We can still win the Premier League and the FA Cup, despite this defeat.
“Nothing has changed for us – we need to work hard but there is a long way to go. We have proved before we can win the title from situations like this.
“We have the players and the spirit to recover and I believe we will still win the Premier League and FA Cup double.”
