Arsenal won their set-piece battle with 10-man Chelsea as Jurrien Timber sealed the Premier League leaders' crucial 2-1 victory over their London rivals on Sunday.
Mikel Arteta's side struck twice from corners and also conceded from the same route in a match that underlined the increasing importance of set-pieces in the Premier League.
William Saliba's first goal since December 2024 put Arsenal ahead in the first half at the Emirates Stadium.
Piero Hincapie's own goal drew Chelsea level from one of Reece James' deadly corners just before the break.
But Timber won a priceless three points for Arsenal with his second-half header before Chelsea winger Pedro Neto was sent off for a second booking.
The Gunners' second successive league win reestablished their five-point lead over second-placed Manchester City, who have a game in hand and had closed the gap with a 1-0 victory at Leeds on Saturday.
After enduring scathing criticism of their mentality during a recent wobble that breathed new life into the title race, Arsenal have got back on track just in time as they followed last weekend's 4-1 rout of Tottenham with a far more tense triumph.
Arsenal travel to Brighton on Wednesday with nine games left in their bid to win a first English title since 2004.
The Gunners, through to the League Cup final, the Champions League last 16 and the FA Cup fifth round, have just one top-flight match left against sides currently in the top six – a potentially decisive trip to Manchester City on April 18.
Chelsea's third consecutive game without a win was a blow to their bid to qualify for next season's Champions League.
They dropped to sixth place after losing to Arsenal for the third time in Liam Rosenior's brief reign.
Robert Sanchez nearly gifted Arsenal an early goal when the Chelsea goalkeeper stumbled under pressure from Viktor Gyokeres, but he managed a last-ditch clearance to avert the danger.
TIMBER MAKES HIS MARK
When Sanchez gave the ball away with another nervous clearance, Rosenior held his head in frustration.
Arteta prayed on Chelsea's weakness at the back to take the lead with one of set-piece coach Nicolas Jover's trademark routines in the 21st minute.
Gabriel Magalhaes towered above Reece James and Joao Pedro to nod Bukayo Saka's corner into the six-yard box, where Saliba's goal-bound header deflected in off Chelsea's Mamadou Sarr.
Chelsea have conceded eight goals from set-pieces in Rosenior's first 13 matches and four of those have been against Arsenal.
But the Blues got their revenge on the stroke of halftime.
Arsenal were given a warning when James' corner hit Declan Rice's shoulder, forcing David Raya to make a superb save.
But they didn't learn the lesson and from the resulting corner, James' inswinger was headed into his own net by Hincapie.
Arsenal remained vulnerable from James' corners and Joao Pedro should have done better than head straight at Raya before nodding wide from another of the Chelsea captain's teasing set-pieces.
Those misses proved costly for Chelsea as Arsenal once again showed their own set-piece prowess in the 66th minute.
Timber made a perfectly timed run to head home from Rice's corner, with Chelsea's furious appeals for a foul on Sanchez failing to get the goal overturned.
It was the 16th league goal scored from a corner by the Gunners this season and their jubilant fans celebrated by chanting "set-piece again, ole, ole".
Neto, booked for protesting in the aftermath of Timber's goal, rashly took out his frustration on Gabriel Martinelli, chopping down the Arsenal winger to earn his marching orders in the 70th minute.
Arsenal still needed a brilliant stoppage-time save from Raya to deny Alejandro Garnacho before they could celebrate.