Paik Seung-Ho scored his first goal since December to give Birmingham a 2-1 victory over Derby at Pride Park.
Bobby Clark put Derby ahead only for Carlos Vicente to reply minutes later and Seung-Ho won it after a lengthy stoppage for what looked like a serious injury to Derby's Henrik Meister.
Birmingham had looked the sharper side in the first half and a quick break in the 23rd minute left Derby short at the back and Vicente cut inside to unleash a shot which went narrowly wide.
Eiran Cashin almost gifted Birmingham a goal in the 29th minute with a back pass which Jacob Widell Zetterstrom just kept out with his right foot.
Derby were in trouble three minutes later when a poor clearance from Sondre Langas fell to Jay Stansfield and his shot beat Zetterstrom but hit the centre-back and bounced to safety.
The home side had created little until the 40th minute when a clever pass by Sam Szmodics found the run of Clark who beat James Beadle at his near post.
But the lead lasted just two minutes as Liam Millar crossed to the back post where Vicente got in front of Charlie Taylor to head in.
The second half was only a couple of minutes old when Meister went down off the ball on the edge of the centre circle. There was a stoppage of around seven minutes while the forward received medical attention before being taken away on a stretcher.
When the game restarted, Derby put Birmingham under pressure, forcing Beadle to turn away a Mo Fuseini shot at full stretch.
At the other end, Alex Cochrane fired in a 20-yard shot which Zetterstrom could only parry and when the ball went behind for a corner, Birmingham scored.
Miller swung the ball over and substitute Seung-Ho, who had only been on the pitch for four minutes, headed in from close range
Derby responded strongly but Birmingham were close to a third when Vicente's low shot was blocked by Zetterstrom, who then made a flying save to deny Stansfield.
Birmingham should have wrapped it up in the 89th minute when Luis Vazquez fired over an empty net from two yards after Ethan Laird's shot had been parried.
With 13 minutes of time added on, Birmingham had to hope that would not prove costly but it needed a goal-line block by a blue shirt to deny Szmodics.
Another block by Christoph Klarer denied Szmodics again and Carlton Morris saw a shot charged down as Birmingham held on.
Derby's John Eustace:
"I thought we were excellent in large parts of the game against a very competitive team. Really disappointed in the two goals we conceded, we need to be better after getting caught in possession and then defending the far post.
"The second goal has come from a long goal kick and it's gone straight between our two centre-halves and we need to be bigger and better at defending that and then from the set-piece we obviously need to be stronger.
"I think we have to adjust and get used to each other as well, it doesn't just come from the back four it comes from the front players as well.
"We're chopping and changing the team a fair bit to try and get the right chemistry and solutions so we've got to keep working hard on the training pitch."
Birmingham's Chris Davies:
"I think I'm right in saying we've got the same amount of points from the same amount of games as we did last season but we've looked a completely different team.
"Not only stylistically but just the strength and mental strength we've shown and the desire. It pains me to say it but we would have lost that game last season or we would have drawn it.
"I think the trust starts to grow in the group. You go to Wrexham and win, you go to Derby and win and it says a lot of what we are capable of.
"I think anyone who plays sport or football knows those wins are the best where you've had to show that real character and grit because it makes victory taste that bit sweeter.
"It was a massive win, a win that had a bit of everything in it in terms of the way we went about it so to win it and win it in the way we did was pretty special today."
