"The derby is always the game of the year," said Mancini, whose side are back in contention of the title after United lost to Wigan and drew with Everton.
"For the supporters, a derby is always a different game to the others. It is important for the city.
"Manchester has two top teams who are in a position to play this important game.
"But for us it will just be one more game, not because we fight for this or for that, and after it there are another two games, very tough games."
Mancini added that whatever happens the season has been a success for City.
"We are happy to be where we are," he said.
"We already have 10 more points than we got last year, and I am happy that we can finish the season well."