Gareth Bale maintained his exhilarating run of scoring form to set Tottenham on its way to a 2-1 win over Arsenal on Sunday, opening up a seven-point gap between the north London rivals in the race for Champions League qualification.
Bale - with his 10th goal in his past eight games - and fellow winger Aaron Lennon scored in a three-minute span at the end of the first half, a crucial spell that proved enough to keep Spurs in third place with 10 games left.
Per Mertesacker's 51st-minute header that deflected in off Bale gave Arsenal hope of a third straight comeback from 2-0 down in a typically absorbing and frantic derby. But the visitors couldn't avoid a costly loss that dents their chances of playing in the Champions League for a 16th straight season under Arsene Wenger.
"It's massive to go seven points clear, in a north London derby,'' Spurs defender Michael Dawson said. "We have a long way to go but it is a good day.''
With Arsenal likely to go without silverware for an eighth successive season, Wenger has been pinning his hopes on a top-four finish to salvage something from a miserable campaign. But even that is in serious doubt now, with Chelsea five points ahead of the Gunners in fourth place. There is no more room for error.
Wenger's side came back from a 10-point deficit to Spurs last season to qualify for Europe's top competition, but Bale wasn't in such scintillating form then.
The Wales winger is virtually carrying Tottenham back into the Champions League on his own, with his latest strike buttressing his strong chances of winning English football's Player of the Year award. It also ensured he equaled the club record - held jointly by Robbie Keane, Rafael van der Vaart and Teddy Sheringham - of scoring in five straight Premier League games.
He had arguably been having his quietest match of the season up until his goal, with Arsenal starting the stronger and its oft-criticized defense looking compact.
It then simply disintegrated.
First, an unchallenged Gylfi Sigurdsson slipped a ball through for Bale to beat the offside trap in a central position before finishing with the outside of his left foot past goalkeeper Wojciech Szczesny. His 20th goal of the season in all competitions was met with chants of "He scores when he wants'' by the delirious home fans.
Arsenal's back line, which has been suspect all season, hadn't learned its lesson because Scott Parker threaded a pass behind the docile Thomas Vermaelen and Lennon rounded Szczesny to slot into an empty net only 140 seconds later.
It will have been extremely disheartening for Wenger, whose team made had its best start for some time. Only a last-gasp tackle by Spurs defender Jan Vertonghen, the game's outstanding player, stopped Olivier Giroud from going through on goal, while the impish Jack Wilshere - playing in a more attacking role - looked more than capable of picking off Tottenham's high defensive line. The team's passing and movement was sharp and crisp.
The frustration had been starting to show on Spurs' players, with former Arsenal striker Emmanuel Adebayor picking up a booking for a rash tackle on Aaron Ramsey in the 18th. Adebayor was sent off in the meeting of the rivals in November, but his game ended early for a different reason here - he was carried off on a stretcher midway through the second half with an apparent right knee injury.
Arsenal came from 2-0 behind to win the last two derbies 5-2, and its fans dared to dream of another comeback when Mertesacker rose highest to glance in a free kick from Theo Walcott that took a touch off Bale. Both of Mertesacker's goals this season have come against Spurs.
More goals have been scored in north London derbies than in any other head-to-head rivalries in the Premier League, so it was no surprise to see them flying in once again.
Bale, who had a banana thrown at him by Arsenal fans in the first half as he prepared to take a corner, missed a glorious chance to make it 3-1 in the 59th when he shot over from close range.
Arsenal was given more lifelines when Sigurdsson chose to pass rather than shoot when one-on-one with Szczesny, and then Jermain Defoe, on for Adebayor, dribbled a shot wide.
The visitors threw everything in the final 10 minutes, but Spurs held on for arguably their biggest win of the season.