It was only Birmingham's second win of the season, but it was well merited on the day as Bolton again struggled to make any real impact.
Following the disappointing 2-0 defeat in their previous game at Middlesbrough this was a major improvement and must have pleased manager Steve Bruce.
Seb Larsson had an outstanding game and was often a thorn in the side of Bolton, who suffered a second-half setback when Jlloyd Samuel had to be stretchered off with a leg injury, following an innocent looking tackle.
Bolton, with only one win in their opening six games, were often disjointed. El-Hadji Diouf was prominent as was Nicolas Anelka when they laid siege to Birmingham in the closing stages as they strived unsuccessfully to force an equaliser.
But Bolton's problems had been evident even in the first half when they found themselves under increasing pressure from Birmingham's reorganised side.
Larsson, in particular, was a major problem and former Aston Villa defender, Samuel struggled to contain the former Arsenal wideman. Larsson deserved a goal and only the woodwork prevented him getting on the scoresheet in the second half.
Bolton could make little impression although Anelka forced Maik Taylor to make a smart near-post save to keep out the Bolton marksman. Newcomer Andy O'Brien, who was making his first appearance, then headed over from close range, as did skipper Kevin Nolan.
Nolan became the first player to be yellow carded when he hacked down Larsson and it was from this incident that Birmingham appeared to lift their game.
Larsson, who had to receive lengthy treatment following the Nolan tackle, appeared to raise his game and it was hardly a surprise that he created the opening from which Birmingham took a 37th minute lead.
Larsson's cross the far post found the lurking Kapo to nudge the ball home from close range despite a desperate attempt by Jussi Jaaskelainen to keep his goal intact.
This goal forced Bolton out of their defensive approach with Diouf often catching the eye with some astute work.
Birmingham, however, held firm with Johan Djourou emerging with an outstanding performance. The on-loan youngster from Arsenal demonstrated his obvious skills in a high-tension game which lifted Birmingham out of the doldrums.