Two goals in the last 10 minutes, after Tommy Mooney had missed a second half penalty, gave Wimbledon all three points.
“We have to improve dramatically on that, it was very disappointing,” said Bruce.
“I thought we were awful in the first half. At least we gave the crowd something to shout about in the second.
“The incentive of a top six place was there for them all and I told them that after the game. They have to show how badly they want that.
“I'm giving everybody a chance.
“But that's the third time on the trot where we haven't turned up in the first half.”
Bruce was critical of the whole team, and refused to single out Mooney for his penalty miss.
“Tommy's our penalty taker and he's scored before this season. But that was the turning point - I don't think we'd have lost if it had gone in,” said Bruce.