Harry Kewell conceded that mistakes at crucial points in Tuesday night's Carabao Cup contest cost the Reds as they fell to defeat at St Andrew's.
The Australian pointed to the first goal of the game as being a turning point - before Che Adams gave the hosts the lead, he believed there wasn't much between the two sides.
"The result is obviously disappointing but the goals come from mistakes," he told iFollow Crawley.
"I actually felt we were in the game before the first goal.
"You can give fouls away but then you have to react, and we didn't. I felt we were fine up until that point but when you switch off against teams like Birmingham City you're going to get punished."
The bright spark on an otherwise disappointing evening was substitute Panutche Camara's goal five minutes from time.
The young forward raced onto a through ball from Billy Clifford and stylishly found the back of the net for his first senior goal - and the Head Coach was full of praise for the forward.
"I felt when Panutche (Camara) came on he was fantastic," he continued.
"It was probably the goal of the night - it was a fantastic finish.
"I think he's got that real love for football. He just loves the game and wants to get out there and play.
"You play the game because you love it and that's exactly what he showed tonight."
iFollow Crawley subscribers can watch Harry's full interview above - and fans can sign up and watch for free by clicking here.