The Italian insisted that the gap was not a fair reflection of how the season has gone and cited the Red Devils' 3-2 win over his side, courtesy of a last minute Robin van Persie free-kick, as an example of their luck.
With Manchester United having overcome QPR in a comfortable 2-0 win on Saturday, the Premier League champions sit 15 points behind their adversaries with a game in hand - that game being a home tie with Chelsea on Sunday afternoon.
Despite the magnitude of the gap, Mancini was adamant that, though they have been performing better than his side this season, United do not deserve to be so far ahead of his Manchester City side.
"Until now, United have been really lucky with everything, they have won a lot of games in the last minute – like against us when they really didn't deserve to win," Mancini told reporters.
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"But we have lost points in games we deserved to win, when we just couldn't score. For this reason, I say this is the difference. Last year we scored a lot of goals up to this point. We're maybe missing 10 goals and maybe seven or eight points."
The 48-year-old was also hopeful that his side can overcome the odds and catch their neighbours as he referred to a previous title, won with Inter after they almost threw away a 14-point lead, by way of proof.
"I remember in Italy being in the opposite situation to what we are now. I was in first place. I was 14 points above Roma at one point and yet we only won the championship in the last minutes in the last game," he continued.
"So it can happen. If United go forward in the Champions League, then the last two months will be hard for them. To lose five points before the [Manchester] derby means they have to lose two games. It's clear that it won’t be easy for us to win the last 12 games, but if we do, it can happen."