Owen Hargreaves' opening goal on his City debut provided the fairytale stuff, but the practicalities of this bread-and-butter Carling Cup will be more important to Roberto Mancini.
A year ago his bold team selection could not withstand a fired-up West Brom and crashed out at the first time of asking. This new mixture still rested stars but got the job done perfectly well.
The cheer that greeted his 17th-minute strike, after the ball obligingly returned to him from a blocked pass, was genuinely heartfelt for a player who has been through so much these past three years.
It was the England midfielder's first goal since he scored against Arsenal in April 2008 for our neighbours, and he could have been forgiven for celebrating more rapturously than he did.
Instead he savoured the moment, having lamped a cracking shot beyond Birmingham keeper Colin Doyle, and was surrounded by his new team-mates and, later, afforded a warm ovation from a smitten crowd.
Hargreaves' goal was more than welcome too, as a deterrent to the tie drifting towards an impasse, for there had been little incident of note to persuade fans they had made the right decision.
Birmingham, fielding only one player - Keith Fahey - who was in the starting line-up that beat Arsenal at Wembley in February, did come close an equaliser after 35 minutes.
Visiting skipper Curtis Davies surprisingly beat the extra-tall Pantilimon to a hoisted free kick but the centre-back's header was cleared off the line by Kolo Toure, back from his diet pill ban.
A couple of minutes later City had one foot in the fourth round as Balotelli connected with a low Aleks Kolarov cross to send his near-post shot into the far corner
Balotelli greeted his goal with typical straight face, but he was in playful mood and almost pinched a second goal in the second half with a cheeky lob that only just cleared the crossbar.
Carlos Tevez, still not looking like his old self, had the chance to make the score more emphatic before the end but his solo breakaway ended with the keeper saving, a scenario hard to imagine last season.
It hardly mattered. Mancini was able to complete a satisfying night by introducing Dutch teenager Karim Rekik and 20year-old Italian striker Luca Scapuzzi towards the end of a tie that was never in danger.