City's defeat by Tottenham last weekend gave Manchester United the chance to reclaim the trophy against Aston Villa on Monday, and they coasted to a 3-0 win.
Mancini said: "It doesn't change this. They deserve to win this title because they won a lot of games in a row. The crucial moment was when we played QPR, Liverpool, Southampton.
"That moment we had big problems with our players injured. We lost key points. United have more attitude than us, as a club, as a team."
It has long been simply a matter of when rather than if United would clinch a 20th top-flight title, which made the moment itself less hard to take for the City boss.
The Italian said: "It was over three, four, five games ago, not mathematically but it was over. They deserve to win this title, many congratulations to Manchester United for the work they did this season.
"They did better than us, they won a lot of games in a row, it was really difficult. We should be also realistic. If there is one team that did better than you, you can do nothing."