Tottenham Hotspur opened up a seven-point lead over Arsenal with 10 games remaining in the Premier League following a 2-1 victory in the North London derby at White Hart Lane.
Spurs profited from two moments of lamentable defending from the Arsenal back four, with Gareth Bale and Aaron Lennon skipping through a static defence to beat Wojciech Szczesny twice in the space of two first-half minutes.
Contemplating a defeat that would be hugely damaging to their Champions League aspirations, Arsenal responded after 51 minutes when Per Mertesacker saw his header from a free-kick take a big deflection off Bale and nestle in the net.
However, Spurs saw the game out professionally to make the prospect of finishing above Arsenal for the first time since 1995 a distinct possibility. Arsene Wenger's side are left stranded in fifth - five points behind Chelsea and a further two behind Spurs.
Spurs, unbeaten in 11 league games, made two changes as Benoit Assou-Ekotto and Gylfi Sigurdsson came in for Steven Caulker and, more surprisingly. Lewis Holtby; Arsenal's only tweak was the replacement of Abou Diaby with Aaron Ramsey, who along with Mikel Arteta was tasked with keeping an eye on the roaming Bale.
The Welshman had nine goals in his past seven games but initially Arsenal managed to keep him subdued as they enjoyed an impressive start, especially for a team that has begun slowly so many times this season. Pressing earnestly and contesting every loose ball, they put Spurs firmly on the back foot in the white half of North London.
Olivier Giroud was a prominent, if wasteful, figure in the opening minutes. The France international connected with one corner from Jack Wilshere to test Hugo Lloris and was then guilty of hesitancy when controlling superbly from a Arteta pass to waste a fine opening, Jan Vertonghen racing back to slide in and block.
With Emmanuel Adebayor serving a reminder of his early dismissal in the first game between the two sides this season - a 5-2 win for Arsenal - as he slid in on Aaron Ramsey late to earn a booking, Spurs looked to have been rattled by their rivals. However, in two minutes they completely transformed the nature of the game with two goals from their only two shots of the half.
On 37 minutes, with Mertesacker out of sync with his fellow defenders as part of a recklessly high line and playing Bale onside, the Welshman burst through to meet a fine pass from Sigurdsson and took it superbly, allowing the ball to run into his path and poke it past the stranded Szczesny.
Two minutes later, the brittle Arsenal defence cracked open again. This time Scott Parker was the provider and Lennon the finisher, but the concept was the same, the former dinking a neat pass through to the latter, who raced past a static, high back four to round Szczesny and make it 2-0.
Arsenal required a quick response in the second half and they got one inside six minutes of the restart. Ramsey showed great persistence to win a free-kick in an advanced position on the right, and after getting in front of Bale to meet Walcott's delivery, Mertesacker saw his flicked header take a big deflection off the Welshman to sneak past Lloris for an own goal.
Nacho Monreal also fizzed a shot just wide and both Wilshere and Giroud almost connected with a fine cross from Carl Jenkinson as Arsenal upped the pressure again. However, Spurs soon wasted a fine chance to open up a two-goal lead again when Bale somehow side-footed the ball high into the air at the back post when meeting a cross from Sigurdsson.
The traditional derby flare-up occurred on 65 minutes when Tottenham captain Michael Dawson - angry at Arsenal's refusal to play the ball out with Adebayor injured, and perhaps forgetting Spurs also chose to play on with Cazorla down for their second goal - became involved in a bout of shoving with Vermaelen. Adebayor was forced off on a stretcher, having fallen heavily, and was replaced by Jermain Defoe.
Arsenal had made a change of their own as Jenkinson was replaced by Tomas Rosicky, with Ramsey moving to right-back. The tactical tweak did not help their cause in defence as Defoe dragged a shot wide, Bale slammed a volley into the chest of Szczesny and, most dangerously, Sigurdsson opted to cross instead of shot after losing Ramsey and rounding the Arsenal keeper - only to see Mertesacker clear.
A hectic, breathless derby match witnessed a tense conclusion as Arsenal threw everything they had at Spurs. Ramsey dragged a shot wide and substitute Lukas Podolski had a shot deflected over, but the home defence, marshalled superbly by Vertonghen and Dawson, kept Arsenal at bay.
Tottenham duly extended their unbeaten run to 12 league games - their best since 1984-85 when they finished third in the table.
MAN OF THE MATCH
Jan Vertonghen (Tottenham) - A fine challenge to deny Giroud in the first half set the tone and the Belgian, in contrast to compatriot Vermaelen, excelled throughout.
ARSENAL: Szczesny 5, Jenkinson 6, Mertesacker 5, Vermaelen 5, Monreal 5, Arteta 6, Ramsey 5, Walcott 5, Wilshere 6, Cazorla 6, Giroud 5. Subs: Rosicky 6, Podolski 6.