Thibaut Courtois held his hand up after gifting Swansea an equaliser in Chelsea's 2-2 draw in south Wales on Sunday.
The Belgian needlessly brought down Gylfi Sigurdsson inside the area with the Blues leading by a goal to nil thanks to Diego Costa's strike.
The Icelandic striker buried the resultant spot-kick and 210 seconds later Leroy Fer nipped the ball off Gary Cahill, despite referee Andre Marriner missing a foul, to put the Swans in front.
Diego Costa rescued a point for Chelsea with nine minutes from time but the Blues will feel three was what was deserved.
Courtois said: “We're very disappointed. We were very good in the first half. We scored early and we made chances.
“In the second half they had a good counter attack. They played the ball to the striker. I thought I could reach the ball first but it bounced and then I tried to recover and gave away the penalty. It was a little bit stupid but okay.
“They scored and I think the second was a clear foul on Gary. They were trying to defend and we got back to 2-2 and we had occasions to win the game. Unfortunately we couldn't win but our reaction was good.”
Cahill was absolutely furious with the decision not to penalise Fer and the Belgian goalkeeper felt it was a 'strange' call.
Courtois added: “He's very disappointed with the decision. He maybe could have played the ball back earlier to me but you can see Fer hits him twice in the legs and doesn't get the ball. It was a strange decision. It cost us 2-1 and then changed the game.”
