Thibaut Courtois accused Watford winger Gerard Deulofeu of diving to win a penalty as Chelsea were thrashed 4-1 at Vicarage Road in the Premier League.
Chelsea were already down to 10 men after Tiemoue Bakayoko was shown two yellow cards by referee Mike Dean in the space of five minutes.
Soon after, Deulofeu ran through on goal and tumbled over the onrushing Courtois, Dean pointed to the spot and Watford captain Troy Deeney smashed in the spot-kick to give his side the lead.
Eden Hazard levelled for Chelsea before late goals from Daryl Janmaat, Deulofeu and Roberto Peyreya wrapped up a memorable victory for the Hornets - Javi Gracia's first in charge of the club.
But Courtois was unhappy with key decisions made by Dean, suggesting Deulofeu had deceived the official when he went to ground, as well as criticising the decisions that led to Bakayoko's dismissal.
"The red card is very light, first never a yellow and the second too light, obviously the penalty is a clear dive," Courtois told Sky Sports.
"Yesterday [in Liverpool and Tottenham's 2-2 draw] we saw when the goalkeeper comes out and is late you make yourself small but the striker puts his foot there and it's a penalty, every time this will happen. He left his foot and dives, it's not a penalty.
"I think we all know this kind of players it happens everywhere in the world, this type of striker sees the goalkeeper coming for the ball, I make myself as small as possible with my belly on the ground and he manufactures the contact. I'm sorry but I don't think it's a penalty."
Chelsea have now lost successive Premier League matches by a three-goal margin, piling the pressure on under-fire boss Antonio Conte, but Courtois said it is up to the players to respond to their latest setback.
"I think we played a good game against Arsenal after new year although conceded in last minute," the goalkeeper said.
"It's hard to find positive results since two losses and we have to find our form again and get better.
"We have a tough month coming up and we need to pick up points, the Champions League [last-16 tie with Barcelona] is coming soon and we have to continue to work."
