The Blues drew 2-2 at St Andrew's but needed a Papa Bouba Diop equaliser eight minutes from time to prevent Palace from going top of the Championship table.
Glenn Murray's brace had put the visitors two-nil ahead on the hour before Nikola Zigic pulled a goal back on 66.
But Clark remained disappointed despite the fightback: "I didn't think there was much in the first half. We gave away an awful first goal when we didn't compete on the edge of their box.
"Their second goal was something we had discussed all week. We didn't track the run and this was down to simple basics.
"When we were looking down the barrel we have once again produced the half an hour performance that enabled us to get back into the game and potentially win it.
"We were in the ascendancy at the final whistle and I've just said to the players 'Why can't we play like that from the first whistle?'
"We appear to have the shackles on when it's nil-nil. We do not play with the freedom we show when we have to come from behind.
"And I think there was only one team going to win it when the final whistle went."