Olivier Kapo earned Birmingham their first home win of the season as Sammy Lee's struggling Bolton were beaten 1-0 at St Andrews.
Kapo settled the issue when he turned home a cross from Sebastian Larsson.
Blues deserved their second success of the season, but the Trotters remained anchored in the relegation zone after losing for the fifth time in six matches.
Cameron Jerome came close to giving Steve Bruce's side the lead after only two minutes, but his shot dribbled wide.
But after 37 minutes City broke the deadlock through Kapo's second goal of the campaign.
Larsson sent over a deep superb left-footed ball towards the far post and Kapo stuck his foot out and steered the ball past Jussi Jaaskelainen.
Larsson crashed a free-kick against the crossbar late on and Johan Djourou then had a header cleared off the line by Gavin McCann.