The Citizens have dropped off the pace in recent weeks, drawing with Liverpool and Queens Park Rangers, while the Red Devils were victorious against Fulham and Southampton.
City trailed United by eight points in the title run-in last season before overturning their derby rivals’ lead and winning their first top-flight crown in 44 years.
Despite Sir Alex Ferguson’s side looking strong at the league’s summit, Mancini feels anything can happen in the final months of the season, claiming that the Red Devils could struggle to compete on three fronts.
“They have nine points more than us because they did better than us. But in three months, everything can change like last year,” said Mancini.
“If we can recover eight points in six games, I think to recover nine points in 13 games will be easy.
“If Manchester United draw or [have a] defeat, the title race is reopened. It is clear we need to do better than in the last two games.
“It is normal when you play in the Champions League against Real Madrid, you can lose your strength in this game. We support Manchester United to go through in the Champions League.”
Mancini also believes City have been the best side in England over the past couple of seasons, despite Chelsea winning the Champions League last May and United currently leading the title race.
“I don’t think in these two years there is a team that has played better than us,” added Mancini.
“Manchester United are a strong team and Chelsea are a strong team but I think in the last two years Manchester City are the team that played better in the Premier League.”
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