Two goals from former United striker Carlos Tevez secured a 2-1 win for City in the 1st leg at Eastlands on Tuesday night but Mancini refused to single out individual performances after the game.
"Tonight, Carlos played very well. But I think the whole team is more important than one player," the City boss said after the match.
"It is not a big advantage, but it is an advantage.
"I am happy with the result because we were behind after 20 minutes and I felt it could be difficult. But we recovered, scored two goals and played well.
"They had three or four chances but, in Shay Given, we have one of the best goalkeepers.
"At Old Trafford we will start at 2-1, but we know that it will be a hard game.
"We can win at Old Trafford, or we could draw, it is possible."
"I would say we have a 51% chance."