The Hammers thought they’d grabbed a late equalizer from Maxwel Cornet after the Blues had gone ahead from Kai Havertz’s 88th-minute goal.
But the VAR intervened, deeming that Jarrod Bowen had fouled goalkeeper Edouard Mendy in the lead-up, with Cornet swooping on the loose ball to net.
“You have seen it, it is a scandalous decision,” Moyes said.
“Absolutely rotten from one of the supposedly elite referees - it doesn’t say much about whoever sent him over from VAR as well - it is an unbelievable decision against us.
“We feel we got back to 2-2 and it was not down to anything we have done. I support a lot of the VAR stuff, I actually think the goalkeeper dives, he is faking an injury because he cannot get to the next one - he did the same on the first goal as well.
“The referee somehow gets that so wrong it is incredible.”
Chelsea boss Thomas Tuchel claimed it was a “clear foul” on Mendy.
“It was a clear foul on the goalkeeper,” he said.
“I had doubts about the first one but I will not comment, last time I got punished with huge fines. You give your opinion, you will not be fined.”
Elsewhere, Manchester City were held to a 1-1 draw at Aston Villa with Erling Haaland netting his 10th goal of the campaign.
Liverpool also dropped points, held 0-0 in the Merseyside derby away to Everton where both goalkeepers were outstanding.
Tottenham withstood late pressure to win 2-1 over Fulham, while Newcastle United and Crystal Palace played out a goalless draw.
Brentford thrashed Leeds United 5-2, Wolverhampton toppled Southampton 1-0 and Bournemouth rallied from two goals down to win 3-2 at Nottingham Forest.