Mancini has repeatedly written off City's chances of winning the Premier League over the past three weeks, even though they have cut United's lead from eight points to three.
Victory in possibly the most eagerly-anticipated Manchester derby of all-time would take City back to the top of the table on goal difference with two games remaining, but Mancini is still publicly downbeat.
When asked if he was surprised United had allowed City back into the race, Mancini said: "I am not surprised because in football, until you finish the championship or every game, anything can happen.
However, Mancini is in agreement with his United counterpart, Sir Alex Ferguson, over the importance of the encounter.
Ferguson has described the match as the "derby of all derby games" and the biggest encounter with their city neighbours he has been involved with.
"I agree," Mancini said. "I think that after 50 years, Manchester United and Manchester City are playing for the title. For this reason I agree with him."
Meanwhile, Martin O'Neill, the Sunderland manager, has reminded Mancini of City's record against his club after the Italian suggested United's run-in was not as difficult as his side's.
O'Neill's side defeated City 1-0 at the Stadium of Light in January and clinched a 3-3 draw at the Etihad Stadium at the end of March - the hosts scoring twice in the last five minutes to secure a point.
O'Neill, quoted in the Daily Telegraph, said of Mancini's comments: "It took me by surprise because I had to check that the teams they [United] have to play beat Manchester City, like Swansea and ourselves.
"We have taken four points off Manchester City, but they have actually lost five [points] against us this season. He had obviously forgotten to check the fixtures list properly. I will remember it for the next four years. I don't have an email address for him, but I really thought about sending him one to tell him to keep an eye on what he says in the future."
Whether Mancini's comments were merely aimed to rile Sunderland and get them to prove a point against United or not, O'Neill said they showed a lack of understanding of the English game.
"I don't know what his insinuation was," he said. "But if he had any idea about the league at all he would know that the integrity of the league is pretty good."
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