Cardiff City boss Steve Morison told BBC Sport Wales:
"We were excellent, first half tremendous, we should have scored at the start of the second half and then we went a bit flat.
"They got half a foothold in the game, but the changes (substitutions) worked in our favour.
"We should have had a couple more [goals] but we won.
"One of the key aspects is to limit other teams and we limited Birmingham to a very low chance of scoring.
"I'm pleased as punch sitting here, if we had a draw I'd be fuming right now."
Birmingham City boss John Eustace told BBC Sport Wales:
"I am disappointed with how we started the game, we were much better from half an hour onwards.
"I was really pleased with the reaction at half-time, we were much more competitive and much more like ourselves.
"I thought we should have had a penalty, but so should Cardiff probably, so it balanced out.
"There are no excuses. We weren't at the races for the first half an hour… and that has cost us."