Birmingham regained top spot in the Championship from Derby by beating their promotion rivals thanks to a goal from striker Rowan Vine.
Vine scored his first goal for Birmingham against Derby
Vine received a pass with his back to goal before turning and shooting into the bottom corner just on half-time.
But Birmingham suffered a setback when Gary McSheffrey was red-carded for a two-footed lunge on Dean Leacock after 72 minutes.
Derby pressed for an equaliser but the Blues resolutely held on for the win.
There was plenty of concern about the poor St Andrews pitch before the game but it proved better than expected and did not stop an open game.
Both sides had early sighters of goal, including a chance for Blues left-winger McSheffrey.
He pounced on a Dean Leacock mistake only to be denied by on-rushing Rams keeper Stephen Bywater.
Bywater also came to his side's rescue when he spread himself well and saved with his foot after Nicolas Bendtner produced a burst of pace to give himself space to shoot.
Derby striker Steven Howard was a troublesome customer for the Blues defence with his aerial threat but it was his finesse which almost put them ahead.
He curled in a shot from 25 yards and was just wide.
The opening half looked set to end goalless but Vine produced a clinical piece of finishing for his first goal since his move to the club from Luton.
Derby were disappointing for the most part and were comfortably held at arm's length by Birmingham as the game progressed after the interval.
But McSheffrey's dismissal for a rash challenge gave the visitors hope of salvaging something from the game and they tried to pile on the pressure.
Rams boss Billy Davies sent on striker Paul Peschosolido, who is married to Blues managing director Karren Brady, to boost his attack but they failed to break down a stubborn home defence.
Birmingham manager Steve Bruce:
"In the big scheme of things we are delighted to win but there are still 10 games to go.
"In this division anybody can beat anybody but we have given ourselves a great chance.
"We have been resilient over the past month or so. We're in pole position and cannot ask for any more than that."
Derby boss Billy Davies:
"I don't view it as a setback at all. My personal target before the games at Norwich (in midweek) and Birmingham was to get a point at each.
"We won at Norwich and this was a very evenly fought match.
"I feel the fact that we played three matches in a week compared with their two was a crucial part in the outcome of the game."
Birmingham: Doyle, Kelly, N'Gotty, Martin Taylor, Sadler, Larsson (Johnson 90), Muamba, Clemence, McSheffrey, Bendtner (Jerome 79), Vine.
Subs Not Used: Maik Taylor, Forssell, Nafti.
Sent Off: McSheffrey (73).
Booked: Larsson, Muamba.
Goals: Vine 45.
Derby: Bywater, Mears, Moore, Leacock, McEveley (Peschisolido 81), Teale, Oakley (Lupoli 70), Jones, Barnes, Howard, Macken (Bisgaard 53).
Subs Not Used: Grant, Edworthy.
Booked: Oakley, Mears.
Ref: S Bennett (Kent).