Bacuna earns Wayne Rooney first points on the road for Birmingham
It puts an end to eight consecutive away losses for the Blues.
Birmingham manager Wayne Rooney claimed his first points away from home with a 1-0 win at Cardiff in the Championship.
Juninho Bacuna's goal on the stroke of half-time proved enough to decide an entertaining encounter at Cardiff City Stadium that was low on quality.
The result ends a run of eight away defeats in a row for Birmingham and five for former England striker Rooney since taking over at St Andrew's in October.
Victory sees Blues move up two places to 16th, while Cardiff missed the chance to climb up to seventh and stay in contention for the play-off places, instead dropping to 10th.
Siriki Dembele tested Runar Runarsson from a tight angle in the early stages before Birmingham's midfield pair carved out a chance for Jay Stansfield but the Fulham loanee fired his effort across goal.
Cardiff lost defender Perry Ng to a head injury - he was replaced by Mahlon Romeo after just 13 minutes - but had plenty of chances of their own in a lively first half.
Birmingham goalkeeper John Ruddy almost put the ball into his own net when he failed to gather a high ball and forward Kion Etete twice shot over the crossbar from Yakou Meite deliveries.
Ryan Wintle was also a threat with his set-piece deliveries as Dimitrios Goutas' header had Ruddy scrambling low to his right.
Birmingham's Lee Buchanan and Cardiff's Etete both fired efforts over the crossbar as both teams continued to create chances, so it was no surprise that the first half should provide a goal in the third minute of added time.
Cardiff felt Etete was fouled when he lost possession but referee Stephen Martin waved play on and Birmingham took off upfield.
Jordan James and Dembele combined to release Bacuna who calmly rounded the onrushing Runarsson to finish into an empty net.
Cardiff began the second half on the front foot but had two early penalty appeals waved away by Martin and boss Erol Bulut was forced into early chances with the introduction of Callum Robinson and Josh Bowler.
However, it was Birmingham who looked most likely to grab a second.
Stansfield timed his run perfectly to break the Cardiff offside trap but his tame effort went straight into Runarsson's hands.
Moments later and centre-back Emanuel Aiwu snatched at a chance from five yards after James fired in a volley.
Cardiff gradually ran out of ideas and energy, though Rubin Colwill had a chance to snatch a draw with the final effort of the game only to fire his free-kick straight at Ruddy.