Robin van Persie rocketed Arsenal back into the English Premier League title race with a quickfire double that stunned leaders Chelsea in a 2-1 away win at Stamford Bridge on Sunday.
In a keenly-contested London derby filled with end-to-end action, the Blues were 1-0 up thanks to Switzerland defender Johan Djourou's 30th-minute own goal.
But Netherlands striker Van Persie, making his 100th start for the Gunners, equalised with a controversial offside goal in the 59th minute and stunned the hosts with a second goal three minutes later.
Arsenal's title hopes would have been dealt a severe blow by a defeat that would have left them 13 points off the pace and having suffered three consecutive league defeats.
But the manner of their victory at what was the most difficult ground in England to win at will have surely sent notice to the likes of Manchester United and Liverpool that the Gunners are in no mood to give up the race.
Chelsea, who had not been beaten at home in the league for 86 games before their 1-0 defeat to Liverpool on October 26, have now lost two of their last four Premier League ties at Stamford Bridge.
The result means Arsenal are in fourth place, seven points behind the leaders ahead of second-placed Liverpool's match at home to West Ham on Monday.
Chelsea had the better of the opening exchanges and striker Salomon Kalou was played clean through on goalkeeper Manuel Almunia in the fourth minute but his run was ruled offside.
Almunia had to punch twice to clear a cross soon after and former Gunners striker Nicolas Anelka fired another early shot wide.
However, Arsenal swiftly replied and Blues goalkeeper Petr Cech did well to stop a low shot from Samir Nasri before Denilson blazed a shot over the crossbar in the 16th minute.
Chelsea full-back Jose Boswinga jinked through the Arsenal right flank but fired over the bar two minutes later.
Almunia had to be alert in the 21st minute when Deco played Kalou clean through with an excellent pass, charging out of his penalty area to clear the danger.
Frank Lampard then wasted a great chance, firing a free header from Boswinga's cross straight at Almunia.
However, the Blues did not have to wait long to open the scoring.
Almunia caught a Lampard corner and casually rolled the ball out, with Chelsea easily recovering possession. Boswinga crossed in low from the right and Djourou slid in, inadvertently sending the ball beyond Almunia.
Kalou could have doubled Chelsea's lead five minutes before the break. Anelka flicked on a header into the box but Almunia was quickly off his line to gather Kalou's shot.
Denilson then miscued a chance to equalise at the other end, firing his shot over the bar.
Lampard wasted a good chance to kill the game six minutes after the break when Arsenal failed to clear their lines, but he screwed his shot wide of the post.
But within minutes, Chelsea's hopes of sealing victory were crushed by Van Persie's rapid brace.
Chelsea were the only side in English professional football not to have conceded a second-half goal in a league game this season before the Dutchman hit the target with a controversial strike.
Emmanuel Adebayor won a header which Denilson chested down before playing Van Persie through.
The striker, half a yard offside, blasted his shot past Cech to level the match 59 minutes in.
And if that stunned the hosts, worse was to come three minutes later as the Dutchman fired in his second.
Gunners captain Cesc Fabregas played a free kick into the penalty box which Adebayor headed back across goal for Van Persie.
With his back to goal, Van Persie turned Lampard and blasted his shot in across Cech to shock Stamford Bridge.
Chelsea boss Luiz Felipe Scolari threw on forward Florent Malouda in place of John Obi Mikel with 20 minutes to go in a bid to force an equaliser.
The Frenchman fired a free kick over the bar in the 77th minute and Deco shot likewise four minutes later as the hosts urgently sought a leveller.
Scolari then brought on pacy winger Miroslav Stoch in place of Deco but the academy graduate could do nothing to alter the outcome as Arsenal successfully hung on to send a message to the rest of the Premier League that they are still in the title race.