Captain David Marshall bemoaned "two points lost" after Cardiff were held to a 1-1 draw by 10-man Charlton.
The Bluebirds took an early lead through Tom Adeyemi and the Addicks had Callum Harriott sent off before the break for a tackle on Craig Noone.
Johann Berg Gudmundsson equalised, and goalkeeper Marshall had to pull off a late save to keep the score level.
"We played very poorly in the second half because we were comfortable in the first half and played well," he said.
"In terms of how the game went in the second half perhaps Charlton deserved a little more, but in terms of the first half and us having a one man advantage, it's definitely two points lost."
The Scotland international added that he was particularly disappointed by Cardiff's failure top build on a good first half performance.
"We played very poorly in the second half because we were comfortable in the first half and played well," he added.
"At half time we spoke about keeping things the same, doing what we'd been doing and keeping doing the things that had been hurting Charlton.
"We have to stick to what we're good at and we've probably come off that a bit and it's disappointing.
"But we were not as good on the ball, I didn't think we pressed as well as a team."
The result leaves Cardiff 10th in the Championship table, ahead of their opponents on goals scored.
They play Watford at the Cardiff City Stadium on Sunday, 28 December.