Arsenal collapsed under a second-half fightback by Tottenham Hotspur on Saturday, squandering a two-goal lead to lose 3-2 to their north London rivals in a Premier League cracker.
Tottenham defender Younes Kaboul completed a remarkable turnaround for Spurs with an 86th minute headed winner after goals from Samir Nasri and Marouane Chamakh had given Arsenal a comfortable 2-0 interval lead.
Not only did Arsenal lose at home to Tottenham for the first time since 1993, they also wasted the chance to move above leaders Chelsea who play at Birmingham City later.
Arsenal, who suffered their second successive home league defeat, remain on 26 points from 14 games with Chelsea on 28 and Manchester United, who host Wigan Athletic, on 25. Tottenham have 22 points.
Tottenham looked like extending their miserable record against England's so-called top four to 69 away league matches without a victory but they were transformed in the second half with Gareth Bale halving the deficit and a Rafael van der Vaart penalty levelling it up before Kaboul's late winner.
Spurs manager Harry Redknapp praised defender William Gallas, making his first return to the Emirates since leaving Arsenal at the end of last season.
"William Gallas was top drawer today," Redknapp, who raised eyebrows when he signed the former Arsenal and Chelsea player in August told Sky Sports. "He was superb.
"We were hesitant and didn't get the ball in the first half but we took the game to them after the break...it was a great second half performance."
Redknapp even suggested Tottenham could be contenders for the title. "We are in the race...we can achieve anything. It will be tough but it's open this season."
Arsenal dominated the first half and were ahead after nine minutes when Spurs keeper Heurelho Gomes failed to smother a through ball and Nasri rolled the ball into an empty net.
Chamakh made it 2-0 after 27 minutes after a typical Arsenal counter-attack ended withe Moroccan tapping in.
Jermain Defoe replaced Aaron Lennon at halftime and the England striker enlivened Spurs and his header allowed van der Vaart to pick out Bale who scored with ease after 50 minutes.
Tottenham levelled after 67 minutes when Cesc Fabregas handled van der Vaart's goalbound free kick in the area and the Dutchman beat Lukasz Fabianski from the spot.
Laurent Koscielny fluffed a glorious chance to restore Arsenal's lead when he headed over from point blank range. Kaboul then won it for Spurs when he glanced in Van der Vaart's inviting free kick -- a goal that had Arsenal manager Arsene Wenger booting away his water bottle in rage.