Joe Mason's goal just before the break has given Cardiff City the lead over Birmingham City at St Andrew's.
The game was relatively short on action until Mason pounced inside the area to give the Bluebirds the lead in the 41st minute.
The striker tapped in from close range after Jack Butland had saved from Craig Conway.
Nathan Redmond twice tested David Marshall between the sticks, but the visitors' score-sheet remains spotless so far.