Robin van Persie turned on his old club by scoring the only goal of the game as champions Manchester United beat Premier League leaders Arsenal 1-0 at Old Trafford on Sunday to revive their title challenge.
The Dutchman, who joined United in a £24 million ($38 million, 29 million euros) move in August last year after failing to be convinced about the trophy ambitions of Arsenal, who last won a major piece of silverware in 2005, struck in the 27th minute.
Van Persie attacked a Wayne Rooney corner before flicking his header over Kieran Gibbs on the post and into the net.
This victory, arguably David Moyes's most significant success since replacing the retired Alex Ferguson as United manager, saw the title-holders move to within five points of Arsenal, who themselves remained two points clear of Liverpool at the top.
Had United lost, they would have been 11 points adrift of the Gunners, a gap which even at this stage of the season might have been too large for them to overhaul if they were to have a chance of retaining the title.
"It's been a great weekend -- we've not had many of them," Moyes told Sky Sports. "This was a big result for us, Arsenal have been in terrific form this season.
"Overall, it's three important points," Moyes added.
Arsenal manager Arsene Wenger said a run of challenging fixtures had finally caught up with his side.
"We had to give a lot this week -- Liverpool, Dortmund and here today. I think a draw would have been a fair result."
The only consolation for Arsenal fans on Sunday was that arch North London rivals Tottenham Hotspur also lost 1-0, to Newcastle, earlier in the day.
Victory would have seen Spurs go level on points with Liverpool but it was Newcastle who emerged triumphant following an inspired performance by goalkeeper Tim Krul at White Hart Lane.
Loic Remy scored the game's only goal in the 13th minute.
But that the visitors, fresh from beating Chelsea, took all three points owed much to a brilliant display by Dutch shot-stopper Krul, who produced a hatful of excellent saves.
"I think he is the best Dutch goalie for sure and I think he is one of the best in this league," said Newcastle manager Alan Pardew.
Meanwhile Manchester City saw their away form prove fallible once again as second-bottom Sunderland beat them 1-0 for the fourth season in a row at the Stadium of Light.
Phil Bardsley dented City's title aspirations with a 21st minute curler.
City boast a 100 percent record from their five home league games this season but have now taken just four points from a possible 18 on their travels.
"I am concerned because we are losing too many points away and, of course, that's very difficult if you don't win away to try to fight for the Premier League," said City manager Manuel Pellegrini.
Swansea and Stoke shared six goals in a thrilling 3-3 draw at the Liberty Stadium.
Things were looking bad for the Welsh club when Jonathan Walters and Stephen Ireland scored to put visitors Stoke 2-0 up inside half an hour.
But Michael Laudrup's men rallied through second-half goals from Wilfried Bony and substitute Nathan Dyer before Bony scored again with just four minutes left.
However, with virtually the last kick of the game, Charlie Adam rescued a point for Stoke from the penalty spot following a handball in the box, with the draw taking the Potters out of the bottom three.
Swans boss Laudrup was angered by the penalty award, the Danish great saying: "I have to stand here more frustrated than ever because of a very poor decision.
"I always defend referees and linesmen because they are humans but now I have seen it, there are seven Stoke players inside the box and none of them asking for handball.
"Just one in the stadium saw it and it was the ref."