Palace were in command when Glenn Murray made it 20 goals for the season as he completed his double to make it 2-0 on the hour mark.
But substitute Nikola Zigic and Papa Bouba Diop levelled things up to ensure Lee Clark's men claimed a share of the spoils.
He said: "I think there was only one team going to win it when the final whistle went.
"I didn't think there was much in the first half. We gave away an awful goal when we didn't compete on the edge of their box.
"The 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 said to the players 'Why can't we play like that from the first whistle?'
"Why can't we play with that drive, determination, desire and aggressive running without the ball?
"We appear to have the shackles on when it's 0-0. We do not play with the freedom we show when we have to come from behind."
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