Djibril Cissé and Jamie Mackie scored for the visitors in a frenetic 15-minute spell to cancel out Pablo Zabaleta’s first-half opener, leaving City in second place behind Manchester United.
But substitute Edin Dzeko headed in a leveller in the second minute of stoppage time, before Sergio Aguero burst past the QPR defence and clinically fired home to prise the title from United’s grasp.
“It was incredible,” Mancini told Sky Sports. “You can’t imagine a finish like this. It’s impossible.
“I think we deserved it. It was incredible for me and all our supporters. I’m very happy for them.
“I’ve never seen anything like this. It’s incredible. I don’t know what I can say. Five minutes from the end I didn’t think we could win this game.
“We wanted this title because we deserved this title. We stayed on top for 28 games.
“For us it was really important to win this championship and the future of Manchester City. We can have a big future.
“It was a perfect final game to end a crazy season.”
Kompany, who scored the winner in the Manchester derby back in April, insisted the belief remained in the City side despite waiting until the death to dramatically claim their first top-flight crown since 1968.
“It’s the best moment of my life but if I’m honest please never again this way,” Kompany said.
“We’ve been so good this season especially at home and then all of a sudden today, even though our first half was really good, we couldn’t get through.
“We’ve done it before this season [come from behind] and I never stopped believing. When Edin scored that goal it just reminded me of a few other moments this season against Tottenham Hotspur and Sunderland.
“We’ve done it this season before so we had no reason to believe.”
QPR, who were reduced to 10 men when Joey Barton was shown a straight red card in the second half, avoided relegation as a result of Bolton’s 2-2 draw at Stoke.
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