Arsenal ran riot in east London, putting four past them in a sensational half that saw ex-West Ham captain Declan Rice grab two assists.
William Saliba, Bukayo Saka, Gabriel and Leandro Trossard all got on the scoresheet to stun the Hammers crowd.
And Sky Sports cameras overhead picked up legions of fans leaving the ground and going home before the half-time whistle had even been blown.
West Ham were branded "a disgrace" by Roy Keane in the Sky Sports studio while commentator Alan Smith said: "I can't believe what I'm seeing."
The stands looked visibly empty ahead of half-time, even before Trossard scored in the 47th minute.
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And with cameras overhead picking up swathes of fans leaving the ground, it encapsulates what has been a shocking opening 45 minutes from the Hammers on Sunday.
Arsenal came flying out of the traps and, in truth, could have been further ahead had Saka had his shooting boots on.
But David Moyes, who has already been under pressure this season, will be furious with the manner of which they conceded first.
After several elaborate corners, Rice decided to go old-school on 32 minutes with his delivery and sent a cross towards the back post.
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There, Saliba rose highest and unchallenged to nod home the opener and give Rice an assist against his old club.
Saka was then released after a brilliant ball over the top from Trossard saw the England international one-on-one with Alphonse Areola, who fouled him in the box.
After a lengthy VAR check to see if the 22-year-old was offside, eventually, he dusted himself off to score his 50th goal for the Gunners.
That was on 41 minutes and Moyes might have felt that they could regroup at half-time.
But there was worse to come as another Rice delivery found Gabriel from a free-kick, nodding past Areola to make it three.
Trossard then completed the 45-minute rout with a lovely finish into the top corner after leaving Kurt Zouma for dead.