Manchester United defender Phil Jones "made a meal" of Sofiane Feghouli's challenge which resulted in the West Ham player being controversially sent off, says Hammers boss Slaven Bilic.
West Ham played for 75 minutes with 10 men after Feghouli was shown a straight red card by referee Mike Dean.
Manchester United went on to win 2-0, their sixth straight league victory.
"It was not a red card. Feghouli's foot was not high in the air, it was not deliberate," said Bilic.
Bilic accused England international Jones of going in "dangerously" on Feghouli.
"It was the key decision and it killed us.