David Moyes says the decision to send off West Ham defender Fabian Balbuena against Chelsea was made by someone "who's never played the game".
The result dented the Hammers' hopes of securing a top four finish and a place in the next season's Champions League.
"It was a really poor decision," added Moyes after Chelsea moved three points clear of fifth-placed West Ham.
West Ham trailed to Timo Werner's goal when referee Chris Kavanagh reduced West Ham to 10 men in the 81st minute.
Paraguay defender caught Chilwell's leg with his follow through while making a clearance.