SUB Eddie Nketiah nicked Arsenal's undeserved late winner.
Alexandre Lacazette's firm headed opener had been cancelled out by West Ham livewire Michail Antonio on the stoke of half-time.
Pierre-Emerick Aubameyang underlined his worth after signing a new 350,000 a week contract by surging into the box to cross for Lacazette powerful opener on 25 minutes.
But the Hammers conjured a flowing equaliser.
Jarrod Bowen scampered down the left to feed the overlapping Ryan Fredericks, who pinpoint delivery was swept home by Antonio.
That took the West Ham wideman level with Raheem Sterling as the only Premier League player since June - post lockdown - to net nine goals.
The Gunners faded after that, the visitors in contrast looking increasingly composed.
But Arsenal restored their lead with their first shot since the 47th minute - in which time West Ham had ten.
Lacazette's replacement, Nketiah, was the 85th minute hero. Bukayo Saka fed loanee Dani Ceballos, who set up Nketiah for a simple six-yard finish.
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