The bitter rivals meet at Eastlands on Wednesday night and victory for Mancini's side will move them level on points with United.
But Mancini believes the match will have little effect on the title race as he is adamant Carlo Ancelotti’s side will win the Premier League for a second successive season.
"I think that the Premier League is very long, very difficult,” said the City boss.
“It is important for us to stay in the group for second and third position. I think Chelsea will win the Premier League, but all the other teams that are near them can try.
"In my opinion, Chelsea is better than the other teams. But in football sometimes the winner is not the best team. Our target must be the Champions League. If we are there in January and February we can have a chance (of winning the league)."
Mancini also claimed United are running scared of his side, and is confident City can come out on top on Wednesday night.
"I think that they know that we are a strong team," he added. "The situation has changed.
"We have respect for United, and respect for Fergie because he's the top manager in the world. But we can be better than them always now."