Sergio Aguero's late goal was decisive in the 2-1 win as the first- and second-placed teams in England's top flight put on a high-tempo show that show United's 15-point advantage cut to 12.
United are still odds on to clinch a record-breaking 20th Premier League crown come May, but Mancini says the talent his squad showed at Old Trafford is yet more evidence City can come out on top in future seasons.
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"It is important that we continue to win – we have another seven games. For now we need to play like this. For next season we have two or three months where we can work well and where we can improve our team."
Mancini did, however, admit that United are deserving champions-elect this campaign having tasted defeat for the first time since November on Monday night, but suggested the size of the gap is flattering to Sir Alex Ferguson.
"I think that we showed this tonight. We can't be 15 points behind," he added. "We can say United won a lot of games. They lost their last [league] game against Norwich a long time ago, so they deserve to win this title.
"This win is important for us because it can help us for second position. We deserved to win because we played better. We played good football. We didn't take any risk."
Mancini went on to rue a string of injuries to key personnel over the course of the term, with the likes of captain Vincent Kompany only recently returning from a long first-team absence while David Silva limped out of Monday's derby triumph.
He continued: "This season we had some problems with players injured. We are not a team that can lose three or four players. We can't lose Yaya Toure and Vincent Kompany together. We are not so strong that we can lose three or four players like this."