Eden Hazard set up the decisive goal for Marcos Alonso as Chelsea beat Arsenal 3-2 in a frenetic London derby.
For 20 minutes Chelsea were so good it looked like it would be a rout, with goals from Pedro and Alvaro Morata their reward.
But Arsenal roared back to level through Henrikh Mkhitaryan and Alex Iwobi within five first-half minutes.
Both sides had chances to earn the Premier League points before substitute Hazard, apparently staying put for now after a summer flirtation with Real Madrid, crossed for Alonso to net the winner nine minutes from time.
This had the early prospect of being humiliating for Arsenal and boss Unai Emery in his first London derby.
The Gunners' attempts to play out from the back against champions Manchester City were met with ridicule and there was early cause for embarrassment here - their first goal kick had to be retaken as the pass from Petr Cech to Sokratis Papastathopoulos did not leave the area.
Pedro's pace had caused Sokratis to panic and Arsenal were punished by the Spaniard soon afterwards.
Alonso raced on to Jorginho's pass and centred for Pedro to tuck in with ease.
Pierre-Emerick Aubameyang should have equalised. First he shot straight at Kepa Arrizabalaga after Shkodran Mustafi's fine pass down the right. He then spurned an easier opportunity.
Again Arsenal got in behind Alonso, Matteo Guendouzi finding Hector Bellerin. Aubameyang was on the penalty spot in plenty of space, but lifted the ball over - and Chelsea punished the miss immediately.
Cesar Azpilicueta lofted the ball down the right channel for Morata and the Spain striker, with one league goal in 15 league appearances since Boxing Day prior to this game, turned Mustafi inside-out and then tucked the ball under Cech.
The visiting section experienced an all-too-familiar sinking feeling as Chelsea fans sang 'Are you Wenger in disguise?'.
Arsene Wenger's Arsenal last won at Chelsea in October 2011 and that 5-3 success was the last time they had scored more than once here.
The Gunners continued to create opportunities, spurning them initially.
Iwobi - fully justifying his inclusion ahead of Aaron Ramsey - found Mkhitaryan in plenty of space. Unfortunately for Arsenal, like Aubameyang before him, the Armenian lifted the ball over.
Mkhitaryan made amends after Monreal nipped in to intercept Ross Barkley's pass towards Willian. Iwobi ran at Chelsea, his shot ricocheting back for Mkhitaryan to score.
Mkhitaryan turned provider soon afterwards, crossing for Iwobi to fire in from the position where the Armenian and Aubameyang had missed.
Arsenal should have led at the interval. Aubameyang scuffed the ball onto his standing foot and wide from Iwobi's cross. Mkhitaryan then crossed for Iwobi to blast over.
Chelsea regained control. Some fine individual skill from Barkley created a shooting opportunity for himself, but Cech saved.
Sarri sent on Mateo Kovacic for his debut, for Barkley, and Hazard for Willian.
The Belgian was warmly greeted - many had feared he would leave in the summer - and he aimed to please, controlling an aerial ball as if it were a feather before having a shot blocked with his first real involvement.
Hazard sent a low ball across the face of goal and then a deft flick freed Kovacic, who was felled.
Arsenal were standing firm. Olivier Giroud was sent on, but an Alonso cross was too high for him and dropped to N'Golo Kante instead. Kante headed over.
Chelsea's persistent pressure was rewarded when Arsenal substitute Alexandre Lacazette gave the ball away and then was beaten by Hazard down the left. Hazard pulled the ball back for Alonso to score.
Chelsea might have had more, but for Cech. Hazard bamboozled the Arsenal defence and had a shot saved before Giroud was denied twice.