Manchester United all but sealed a 20th English title as they moved into an eight-point lead over Manchester City at the top of Premier League on Sunday with just six games left to play.
United beat Queens Park Rangers 2-0 at Old Trafford to pile the pressure on City ahead of their match away to Arsenal later Sunday.
But City were unable to respond, with Mikel Arteta's goal three minutes from time securing a 1-0 victory for the Gunners that saw them leapfrog north London rivals Tottenham Hotspur into third place in the table.
City's misery was compounded when temperamental striker Mario Balotelli was sent-off a minute before full-time.
Before kick-off, City manager Roberto Mancini said City had to win if they were to have a chance of being crowned champions of England for the first time since 1968.
"Today for us is like a final, otherwise eight points is too much," the Italian told Sky Sports.
Afterwards Mancini, asked if City's title bid was finished, replied: "Not mathematcially. It's very diffuclt but we will do our best."
Mancini appeared to have run out of patience with compatriot Balotelli, who was sent off after collecting a second yellow card for a foul on Bacary Sagna, having been lucky to avoid a straight red in the 20th minute for a horrible challenge on Alex Song.
"The first tackle was bad," said Mancini. "I defend Mario because he is a good guy but if he doesn't change in the future he could waste his talent. He can't continue to play like this."
At Old Trafford, goals from Wayne Rooney and Paul Scholes saw United - who are now two goals better off on goal difference than City - to victory.
England striker Rooney gave United a 15th minute lead from the penalty spot after QPR captain Shaun Derry was controversially sent off for bringing down Ashley Young inside the area, with referee Lee Mason ruling he'd denied a clear goalscoring chance.
Mason's decision was harsh on Rangers, who are still above the relegation zone on goal difference. Derry's contact appeared minimal and Young looked to be offside.
"I thought it was offside," said United manager Sir Alex Ferguson.
"There have been lots of decisions like that in the last few weeks. The boy (Derry) did just enough to off-balance Ashley and, being the last defender, the referee felt he had no option.
"I felt we were a little bit out of our comfort zone after that, I didn't enjoy it," he added.
"Before the sending-off our speed was terrific, we had some good play, but the sending-off unsettled us and put us out of our comfort zone."
Even though QPR keeper Paddy Kenny correctly dived to his right, Rooney's well-struck penalty gave him his 30th goal of the season and left the visitors, managed by former United striker Mark Hughes, with a mountain to climb.
Kenny kept QPR in the game until the 68th minute when he was beaten by a 20-yard shot from veteran midfielder Scholes, recalled from retirement this season by Ferguson.
Hughes confirmed QPR would appeal Derry's red card in a bid to have him available for Wednesday's match at home to Swansea.
"We'll obviously try and appeal that and hopefully get that overturned by Wednesday," he said. "We can ill-afford to have any more out.
"I think everybody understood that the boy (Young) was offside and that there was minimal contact. The boy has gone over too readily."