Chelsea produced an appalling first-half performance and were crushed in a one-sided London derby.
The Blues, beaten in all six of their matches since Frank Lampard returned as interim boss, were three down within 34 minutes at the Emirates Stadium, where Noni Madueke pulled a goal back in the second half – his first Chelsea goal.
Martin Odegaard curled the opener past keeper Kepa Arrizabalaga and then scored a similar goal, finishing emphatically when Granit Xhaka easily got away Raheem Sterling and crossed for the Norwegian.
Gabriel Jesus capitalised on more diabolical Chelsea defending to make it 3-0.
They failed to deal with Ben White’s cross from the right and Xhaka retrieved a loose ball to tee up Jesus, who netted from close range.
Arsenal continued to dominate after the interval and should have added to their lead before Chelsea pulled a goal back when Madueke scuffed the ball in after sneaking away from Oleksandr Zinchenko to get to Mateo Kovacic’s ball in behind the Gunners defence.
Lampard started with Pierre-Emerick Aubameyang against the striker’s former club but Chelsea again offered very little in attack, and he was replaced at half-time by Kai Havertz.
Chelsea: Kepa, Azpilicueta, Fofana, Silva, Chilwell, Kante, Fernandez (Mudryk 71), Kovacic, Madueke (Ziyech 79), Sterling (Gallagher 71), Aubameyang (Havertz 45).
Subs not used: Mendy, Badiashile, Felix, Loftus-Cheek, Chalobah.