Joleon Lescott went to make a simple headed clearance. Instead, he knocked the ball backward and Djibril Cisse seized on the defender's mistake by driving a shot past Joe Hart.
City's task seemed to be made easier when former player Joey Barton lost his cool and threw an elbow at Carlos Tevez as a cross came into the penalty area from Zabaleta. The QPR captain was seething after receiving a red card and kneed Aguero as he left the field. Both sides had to placate the raging player, who was dragged to the sideline.
Despite City enjoying the man advantage, QPR went in front on a rare counterattack. Armand Traore was given space to go down the left flank. Hen then picked out unmarked Jamie Mackie in the penalty area and he sent a downward header past Hart in the 66th.
Half an hour later, though, City emerged as 3-2 winners and champions of England.
"When we were losing 2-1, I thought, 'We'll score one goal and we're still going to lose,'" Zabaleta said. "I don't want to wake up from this. You just look at the players and the fans, everybody deserves this.
"The most important thing for any team is when you believe. If you believe in yourself you win. We believed until the last minute."
In Sunderland, United's players left the field stunned by what had unfolded. Fans stood with hands on heads in bewildered silence.
"It's a cruel way (to lose the title)," Ferguson said. "We've experienced many ups and downs in the 25 years I've been here, most of them have been great. We've won the title three times on the last day; today we nearly did it."
Associated Press writer Mark Walsh contributed to this report from Sunderland.
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