The Italian watched his side claim a hard-fought 2-1 win over the Red Devils on Monday, with Sergio Aguero scoring a magnificent solo effort to seal victory for the visitors at Old Trafford.
United remains 12 points clear at the top after the result, and Mancini is adamant that finishing above the likes of Chelsea, Arsenal and Tottenham, rather than pushing Sir Alex Ferguson's side in the title race, is all that matters at this point.
"What's important is only for the second position," Mancini told Sky Sports. "15, 12, 18 [points behind] - it doesn't change anything. They scored more points than us [over the season], this is the difference.
"We are happy. It's normal. We played good football - we are happy because we played very well. We deserved to win.
"I think that every time that we play United - in the last game I think we dominated that game and we lost. In the end I don't know how that was possible, but that's football.
"Today's the same. We played football, we played very well, we deserved to win. We only conceded the goal, because we didn't pay attention and didn't mark very well. After that we didn't take any risks."
The City boss went on to insist that his side deserves to be closer to United in the table, saying, "It was important [the victory] for us for the second position, but I think we showed that we don't deserve to stay 15 points behind but this is football.
"They have more authority in this championship, because they've won a lot of games. Instead, we lost points when we deserved to win and we didn't score but today we showed that we deserve to be closer to them.
When asked if the title race was done and dusted, despite City's victory, Mancini concluded: "Yes, it's finished. It's finished."