Cesar Azpilicueta felt referee Andre Marriner missed a "clear foul" on Gary Cahill in the build-up to Leroy Fer's goal as Chelsea were held to a 2-2 draw by Swansea City at the Liberty Stadium.
Chelsea led at half-time following Diego Costa's opening strike, but two efforts in the space of three second-half minutes saw Swansea take the lead.
Gylfi Sigurdsson slotted home a penalty after he was felled in the box by Thibaut Courtois following a break, before Fer dispossessed Cahill and produced a shot that squirmed beyond the goalkeeper.
No free-kick was awarded to Chelsea by Marriner, despite the Dutchman clearly making contact with Cahill and not touching the ball.
An acrobatic second for Costa salvaged a point for Antonio Conte's team, but Azpilicueta was unable to hide his frustration.
"It's a huge disappointment because we had control of the game for most of the time. Their two goals came from mistakes and we were disappointed to only get one point," the Chelsea defender told Sky Sports.
"The second one is a clear foul. The free-kick was clear but the ref made that decision. The reaction of the team was very good.
"At 2-2 we had chances to get a third. The spirit was good but we are disappointed to only get one point."
Azpilicueta believes the effort Costa is putting in on the training pitch is paying dividends after enduring a difficult previous campaign.
He added: "Costa's work in training is reflected in the game. He works hard for the team, makes a lot of movement. If he scores goals, it shows we are doing the right things."
