Alex McLeish was disappointed by the performance of his side during their 5-1 drubbing at Aston Villa.
The derby defeat ensures that Birmingham remain in the relegation zone and their manager accepts that they have not been good enough of late.
"I'm very disappointed obviously," he told Sky Sports.
"They've shown it in the past couple of weeks, their pace ripped us apart.
"I thought we did okay up until they scored and then losing the second goal on half-time was pretty hard to take but we knew we were still in it if we could get something in the second half as long as it stayed at 2-0.
"But unfortunately we shoot ourselves in the foot with some suicidal play at times and Villa were on fire on the day, and let's be honest were a better side than us."
The Blues are now one point adrift of safety and McLeish realises that it is vital that they bounce back at home to Liverpool next Saturday.
"We have to bounce back," he said.
"I don't think anyone expected us to win today though, so it's been a bit of a drubbing to lose five, but they're a long way away from our standard at the moment and they showed that.
"Their agenda is completely different to ours. Ours is to stay in the league, theirs is to try and break into the top four."
McLeish also confirmed that Mauro Zarate's angry reaction to being replaced midway through the second half was purely down to frustration at his own performance.
"I asked him whether it was about the decision and he said it was purely on his performance," he said.
"The players have got to be honest and he's hurt, so if he's doing something like that then it shows you how disappointed he is if you want to question how the players feel about it."
