Derek McInnes' first game in charge of Bristol City ended in defeat as Chris Burke's double earned in-form Birmingham a fifth straight win in all competitions.
It meant another impressive turnaround for Chris Hughton's Blues, who won in Bruges in the Europa League on Thursday and now have a 100% record from their last five games - two of which have been on the continent.
With just one league success against their name all season, the division's bottom club recruited former West Brom player McInnes from St Johnstone on Monday in a bid to turn around a dismal campaign.
But Blues showed no signs of travel sickness at Ashton Gate, with Curtis Davies spurning a golden chance to put them ahead inside a minute, heading wide from a corner.
Nicky Maynard was off target from distance for the home side not long after, but Birmingham looked the more dangerous and Liam Fontaine did well to block a Burke shot, while David James held Keith Fahey's effort.
The former England goalkeeper may now be 41 but he quickly showed he has lost none of his assets, making a stunning double save to keep out Chris Wood - getting something behind two six-yard drives.
