Defeat also piled the misery on new Blackcats boss Niall Quinn in the process.
Sunderland dominated the first half only to be rocked by a penalty disastrously conceded on his home debut by new signing Clive Clarke.
The Wearsiders had been first out of the blocks, with both Liam Lawrence and Daryl Murphy spurning great chances inside the first three minutes.
But the Blues hit back with the type of slick breakaway which typified their performance here.
And Nicklas Bendtner had the ball in the net inside 10 minutes only to see his effort ruled out for offside.
Further Sunderland pressure ensued with further half-decent chances going begging with Murphy and Lawrence again wasting them.
And the Black Cats were rocked when skipper Steve Caldwell was withdrawn injured on 24 minutes, following a collision with City's busy Bendtner.
New Sunderland signing Clarke replaced Caldwell as Quinn's men reshuffled with Danny Collins switching to centre-half and substitute Clarke slotting into the left-back berth.
Clarke received a rousing ovation from the fans but his honeymoon period proved all too brief.
Just nine minutes later a tidy City move saw Fabrice Muamba free Birmingham skipper Damien Johnson in the penalty area.
Clarke had no choice but to make the challenge but in doing so clumsily left referee Graham Salisbury little option but to point to the spot.
And Mikael Forssell stepped up to coolly place his penalty beyond Sunderland keeper Ben Alnwick into the bottom corner.
Sunderland were still reeling from that body blow when they suffered a second on the stroke of half-time.
Lawrence lashed in a shot from the left which finished up in the back of the net but striker Murphy had touched the ball before it crossed the line and was ruled offside.
Despite endless endeavour Sunderland struggled to recover from that double whammy throughout the second half.
Further chances went begging as they sought an equaliser but they'd run out of steam by the end and only a glaring miss from the otherwise very impressive Bendtner denied the Blues a more comfortable margin of victory.