Late goals from Robin van Persie and Thierry Henry saw Arsenal come from behind to earn a dramatic win over Premiership leaders Manchester United.
United went in front when Patrice Evra drilled in a cross for Wayne Rooney to powerfully head in at the far post.
But Van Persie got in behind Gary Neville to slide in Tomas Rosicky's 83rd-minute cross, although he broke a bone in his right foot celebrating.
And in stoppage time an unmarked Henry rose to head in Emmanuel Eboue's cross.
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United had looked like extending their Premiership lead to nine points, with 10 minutes left on the clock.
But Van Persie's sixth goal in seven games pegged them back and Henry stunned the visitors with a late, late winner.
Both managers had predicted an entertaining encounter in the 200th meeting between the clubs.
And in blustery conditions the two rivals produced a game full of intrigue and incident, even if neither side were able to find their top form.
United settled first, with Ryan Giggs and Cristiano Ronaldo both off target as Arsenal battled against the wind in their faces.
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The first flashpoint led to Kolo Toure and Rooney exchanging slaps but, despite both players coming away holding their faces, it did not merit any cards from referee Steve Bennett.
Giggs and Evra both went into Bennett's book for lunging challenges as the game began to simmer.
Henry should have done better than head straight at keeper Edwin van der Sar from an Emmanuel Adebayor cross.
With Arsenal gaining the ascendancy, Bennett looked to have denied them a clear penalty.
Wayne Rooney put Manchester United in front
United thought they had won the game through Rooney's header
With Henry running across the area, Neville stuck a leg out, missed the ball but got the Frenchman, who tumbled to the turf, but Bennett looked to have dodged the decision by neither awarding a spot-kick nor booking Henry.
United finished the half strongly - Rooney and Henrik Larsson both testing Jens Lehmann with headers.
Eight minutes after the break United went in front through Rooney, who was looking closer to his best form even if he was somewhat stifled by having to spend much of the game out on the flanks.
Evra emerged down the left like a runaway train and, with Cesc Fabregas too late to stop him in his tracks, he had time to drill a cross that was gratefully lapped up by Rooney at the back post for only his second goal in 14 games.
Manchester United endured some nervous moments as Rosicky had a couple of stabs at an equaliser before Adebayor instigated a goalmouth scramble that left Van der Sar with a sore mouth.
But that will be nothing compared to the pain United boss Sir Alex Ferguson will be feeling after seeing three valuable points slip away.
Rosicky's centre went under Henry and Van Persie the poacher pounced at the back post to keep their unbeaten home record alive in front of a record Emirates crowd.
But Arsenal were not finished there as Eboue sent in a cross and Henry was left free to thump a header past Van der Sar to the delight of the home fans - and no doubt Chelsea manager Jose Mourinho.
Arsenal: Lehmann, Eboue (Hoyte 90), Toure, Senderos, Clichy, Hleb (Van Persie 67), Fabregas, Flamini (Julio Baptista 79), Rosicky, Adebayor, Henry.
Subs Not Used: Almunia, Denilson.
Booked: Toure.
Goals: Van Persie 83, Henry 90.
Man Utd: Van der Sar, Neville, Ferdinand, Vidic, Evra, Ronaldo (Heinze 90), Scholes, Carrick, Giggs, Rooney, Larsson (Saha 81).
Subs Not Used: Kuszczak, Brown, Fletcher.
Booked: Giggs, Evra, Ronaldo.
Goals: Rooney 53.
Att: 60,128.
Ref: S Bennett (Kent).
