Harlee Dean's header from an 80th-minute Jeremie Bela corner earned the points, but Blues also hit a post through Ivan Sanchez, had a big penalty shout for handball rejected, and saw Robins goalkeeper Dan Bentley save superbly from Ivan Sunjic.

Karanka said: "What I stressed most at the team meeting was that the players needed to have the confidence to express themselves on the pitch.

"There wasn't a lot needed to be said. I have a very good group of players if they believe in themselves and show the right character on the pitch.

"That wasn't the case against Barnsley, but today the performance was so different in every way.

"We were in control in the first half without creating too much and just had to be more of a threat going forward, which was the case after the interval.

"Our goalkeeper has only had to make one save. And after we went in front every player worked so hard to defend the lead.

"The formation is how I want us to play and when you win you are always pleased with the changes you make.

"We were up against a team near the top of the table and beating them should do a lot for the players' confidence.

"Now I expect the same attitude and character in every game. If I get it, we have a team capable of doing good things this season."

After a dull first half in which Birmingham goalkeeper Neil Etheridge made the only save of note to keep out a close-range effort from Callum O'Dowda, the game sprang to life after the break.

Bristol City head coach Dean Holden had no complaints, saying: "There is so little between the teams in the Championship and winning or losing comes down to fine margins.

"We came out on the right side of a close game at QPR in midweek and this time have lost a tight one. That is going to happen because it is the nature of the division.

"We couldn't quite get our final pass right and the first goal was always going to be crucial.

"I'm disappointed to concede from a corner. Dan Bentley has made some fine saves for us and we looked to have overcome Birmingham's best period.

"We don't have a lot of options when it comes to team selection because of all the injuries at the moment.

"But we won't be using that as an excuse and we have to be better. We didn't work their goalkeeper enough.

"We have another home game against Blackburn on Wednesday and need to work on defending set-pieces."

Holden gave a debut to young striker Sam Bell, son of former Robins defender Mickey Bell, as an 87th-minute substitute.

"It was a day Sam will never forget," said Holden. "His dad was a player here and now coaches in our academy so I am sure he is very proud."