Captain Harlee Dean was Birmingham's match-winner in a 1-0 Sky Bet Championship victory over high-flying Bristol City at Ashton Gate.
The centre-back took advantage of poor marking at an 80th-minute corner to rise and powerfully head home Jeremie Bela's cross from the left.
Blues also hit a post through Ivan Sanchez and had a confident penalty appeal rejected in an excellent second-half performance.
The Robins were out of sorts for much of the game and had goalkeeper Dan Bentley to thank for keeping the scoreline respectable.
Head coach Dean Holden made one change from the 2-1 midweek victory at QPR, bringing in Tommy Rowe for Jay Dasilva, while naming young striker Sam Bell, son of former Ashton Gate favourite Mickey Bell, on the bench.
Blues boss Aitor Karanka made five alterations in personnel from the home defeat by Barnsley and switched to a 4-2-3-1 formation.
With midfielders Adam Nagy and Chris Brunt protecting Bristol's back four and Maikel Kieftenbeld and Ivan Sunjic doing a similar job for Birmingham, the first 26 minutes passed without either goalkeeper being tested.
Bristol then created the only worthwhile chance of the first half, Antoine Semenyo's header inside the box setting up Callum O'Dowda for a close-range shot, bravely saved by Neil Etheridge.
Nahki Wells fired over for Bristol City from the corner of the box on 39 minutes, but the whistle for the interval brought to an end a poor half which had seen the teams cancel each other out.
Home skipper Tomas Kalas was in the thick of the action at both ends when the second half got under way.
First the centre-back had a shot cleared off the line by Maxime Colin. Then at the other end he looked fortunate not to concede a penalty when an outstretched arm blocked Marc Roberts' header.
Semenyo fired over as both teams looked to up the tempo. Bentley had to make his first save on 62 minutes, leaping to his left to keep out a swerving shot from Bela.
Suddenly Birmingham were surging forward with confidence. Sanchez hit the foot of the near post with an angled drive before Bentley produced a brilliant save to tip over Sunjic's curling effort from outside the box.
Holden had seen enough and sent on Tyreeq Bakinson for Brunt. Karanka responded by replacing Jon Toral with Alen Halilovic on 71 minutes.
Halilovic was soon involved, sending a low shot from 20 yards narrowly wide, and it was no more than Birmingham deserved when Dean put them in front.
Holden made two double substitutions late on, sending on Bell for his debut, but Blues held out with few alarms.
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