United are currently 15 points ahead of City at the top of the Premier League, and the Italian claims it is down to pure luck.
City have the chance to cut the gap to 12 when they face Chelsea this afternoon, but Mancini is adamant that United's position is a false one.
"Until now, United have been really lucky with everything," Mancini told The Mirror. "They have won a lot of games in the last minute, like against us when they really didn't deserve to win.
"So I don't think the gap between United and us is correct at the moment. They are doing better than us this season, for sure. But we have lost points in games we have deserved to win, when we just couldn't score.
"For this reason, I say this is the difference. We're missing 10 goals, maybe seven or eight points."
Mancini also insisted that the title race is not over, saying that it will be difficult for United in the final months if they reach the latter stages of the Champions League.