London - Eden Hazard came off the bench to provide the winner for Marcos Alonso as Chelsea edged a thrilling London derby 3-2 over Arsenal on Saturday to condemn new Arsenal boss Unai Emery to a second consecutive defeat.
Contrastingly, Chelsea sit top of the embryonic Premier League table thanks to a perfect start under Maurizio Sarri, but made life difficult for themselves after racing into a 2-0 lead inside 20 minutes through Pedro Rodriguez and Alvaro Morata.
Arsenal were level by half-time as Henrikh Mkhitaryan and Alex Iwobi netted.
Yet the Gunners were left to rue wasting a host of other glorious chances before Hazard provided the inspiration in his cameo appearance to swing an enthralling encounter Chelsea's way.
Chelsea cruised to victory at Huddersfield, whilst Arsenal were outclassed by champions Manchester City on the opening weekend of the season.
But given the chasm in quality between their opponents this promised to be a much truer test of where both sides stand in their bid to get back into the top four after missing out on the Champions League this season.
And it didn't disappoint as a thrilling 90 minutes gave both coaches plenty of cause for optimism, but also demonstrated defensive frailties that are likely to prevent a serious title challenge from either side.
Chelsea beat City to the signing of Jorginho to reunite the Italian international with Sarri after three seasons together at Napoli and is already becoming key to Sarri's change of system at Stamford Bridge.
He opened up the Arsenal defence to open the scoring with one pass into Alonso, whose cross was turned into the bottom corner by Pedro.
Despite being outplayed for most of the opening period, Arsenal could easily have scored seven times before the break but for some woeful finishing.
Mesut Ozil flashed a great chance wide seconds before Chelsea's opener and Pierre-Emerick Aubameyang then skied over with the goal at his mercy and the chance to level.
Seconds later, Arsenal trailed 2-0 as Morata raced onto a long ball over the top and turned inside Shkodran Mustafi before firing home his first goal of the season.
Mkhitaryan followed Aubameyang's example by somehow also blazing over an almost identical chance from close range.
The Armenian made amends to spark Arsenal's fightback eight minutes before the break, though, with a fiercely struck low shot that had too much power for the world's most expensive goalkeeper, Kepa Arrizabalaga.
If Kepa could have been questioned for the first goal he has conceded in English football after an 80 million euro move from Athletic Bilbao, he was helpless as Arsenal equalised four minutes later when Iwobi smashed home Mkhitaryan's cross.
There was still time for Aubameyang and Iwobi to pass up another two great chances as Arsenal ended the half on top.
Both sides tightened up after the break as Emery introduced tough-tackling Uruguayan midfielder Lucas Torreria.
But there were still chances at either end as Petr Cech turned Ross Barkley's low effort behind before Aubameyang was unfortunate to be wrongly flagged offside when he did finally find the net.
Sarri believes Hazard isn't yet ready for 90 minutes after his exertions with Belgium at the World Cup.
But he still proved a match winner by easing past Hector Bellerin before providing a low cross for Alonso to sweep home 10 minutes from time.