However, Mancini believes that it is not important how many points they finish behind United as long as they secure second place.
"We are happy. We played well and we deserved to win. We dominated the other game against Manchester United but lost and I didn't know how it was possible. But that is football, today is the same. We played football and we deserved to win," said Mancini.
"It was important for us to get second position but I think we showed we don't deserve to stay 15 points behind. They have had more consistency in this championship because they won more games but instead we lost points when we probably deserved to win.
"We showed we deserved to stay closer to the title but it is finished. It is important we finish in second position. This was important today. Only important is second position, if we lose the title by 15, 12 or 18 points, it does not change anything."
City's next match is against Chelsea in the FA Cup semi-final on Sunday.