Italian saw his side rise to the top of the table once more with its 1-0 win over the Red Devils, but the former Inter man believes the club's rival have an easier final two games
"It is not finished," Mancini told reporters. "If we think it is finished, we will be making a big mistake. United are the favorites."
City tops the Premier League table with a superior goal difference with just two games remaining and has the chance to claim its first top-flight championship in 44 years if the club can match United’s results over the final two games.
City's next game is at Newcastle while United hosts Swansea and Mancini believes their concluding fixtures to the campaign make the Old Trafford side favorites for the title.
"They have easy games. They play against Swansea and Sunderland," Mancini explained. "We have two strong games, Newcastle and QPR. One plays for the Champions League, the other for relegation."
"It is important that we are on the top now but it is more important to be there after May 13."
Sir Alex Ferguson seemed to set his side out in a defensive formation, in the knowledge that a point would keep his team in pole position for a 20th league title and Mancini believes that United was playing for just one point.
"It was important for them to play for a draw because the championship would have been finished," he said.
"We played better. We deserved to win but it was difficult because they had all the players behind the ball."
In four games City has managed to claw back an eight point deficit and Mancini admits the situation is bizarre.
"Football is crazy," he said. "It is important to always believe in yourself when you have a bad moment. We were on the top for 28 games and I think we deserve another chance."
"But in two games, anything can happen."