Top scorer Carlos Tevez weighed in with two more - including the penalty opener - to take his haul to 28 while Emmanuel Adebayor snapped up a brace as the Blues made it 14 in three games.
And lifelong fan Nedum Onuoha scored the other in a man-of-the-match performance he couldn’t have timed better with just a week to go before the derby at City of Manchester Stadium.
City go four points clear of Tottenham, who played in the FA cup, and six clear of Liverpool with a game in hand, leaving Mancini smiling at the prospect of a Champions League campaign.
He said: “I’m happy for the players - we played a fantastic game, and congratulations to them. After 20 minutes we changed the tempo and scored three good goals.
“After three or four months together, you work very well. But I think we can improve more, and we must concentrate on the next five difficult games.
“We must continue to play like we have and at Burnley last week. If we do, we have a good chance. It all depends on us now.
At the moment we are playing good football, like a top-four team, but the Premier League is not finished yet
“We must concentrate in the next game. We respect United as a good team, but we must think about our own position in the table. It’s important that we believe in ourselves.”
Onuoha, being linked with a World Cup call-up by Nigeria, was outstanding at right-back after spending much of the season injured or unable to force his way into the side.
City’s boss said: “Nedum played a good game and scored a very good goal, so I’m very happy for him. He stayed on the bench a long time and I was sorry for him.
“Now he’s playing very well and it’s important he continues. At the moment I’m sorry for Shaun Wright-Phillips - Adam Johnson is playing very well. But we’ll need Shaun and all the players for the next five games.”
