Bryan Hughes and Mikael Forssell scored twice as Birmingham stunned Leeds.
Mark Viduka opened the scoring after some great dribbling and missed a great chance to extend their lead.
Bryan Hughes equalised from six yards and put Blues ahead after a neat lay-off by Stan Lazaridis, while a Martin Grainger free-kick hit the post.
A long clearance put Forssell through for his first and the striker scored from the penalty spot after Stephen Caldwell fouled Clinton Morrison.
After a week of good news off the field at Leeds, the result does nothing for the Yorkshire club's battle against relegation.
United remain lodged in the relegation zone with just eight Premiership games left this season.
The visitors played well through large periods of the game but Birmingham were more clinical with their finishing - scoring four goals in a Premiership game for the first time.
3 mins: Viduka superbly puts Leeds ahead
10 mins: Viduka misses from short range
12 mins: Unmarked Hughes equalises
27 mins: Domi clears off the line from Forssell
40 mins: Grainger's free-kick hits the post
67 mins: Hughes scores again
69 mins: Forssell extends Birmingham's lead
80 mins: Forssell scores from the penalty spot
Leeds caretaker-boss Eddie Gray named the same side that defeated Manchester City on Monday.
And his team made a confident start, creating a flurry of early chances.
Smith's looping header after just two minutes dropped into the path of Viduka, whose volley was well saved by Maik Taylor.
Shortly afterwards Leeds took the lead.
Viduka bent his run to stay on-side and collected Jermaine Pennant's threaded pass before jinking through the Blues defence and slotting the ball into an empty net after evading Taylor.
The Australian should have capped a superb opening phase with a second goal but missed the target from a matter of yards.
James Milner's drilled pass across the face of the Birmingham goal reached Viduka in acres of space at the far post but the 28-year-old directed the ball the wrong side of the post.
Birmingham's equaliser came after Morrison's cross from the right eluded a cluster of players at the near post and broke to Hughes, who had plenty of time to pick his spot.
The Leeds goal came under intense pressure before the break.
Paul Robinson parried a Forssell shot and the Didier Domi cleared off the line after the striker struck the rebound.
Grainger then hit the post with a superb free-kick and Blues' defender Martin Taylor directed the rebound towards the Leeds goal, but Robinson saved.
The game continued to ebb and flow after the break, with Maik Taylor saving from Milner and Viduka as well as almost gifting Leeds a goal.
Kenny Cunningham's back-pass bobbled as Taylor attempted to punt the ball up-field and drifted inches wide of the Birmingham goal with the goalkeeper stranded.
But it was Birmingham who scored next, with Hughes on target again after 67 minutes.
Stan Lazaridis held the ball up superbly in the Leeds area and laid it off for Hughes to coolly finish past Robinson.
Leeds' afternoon generated further minutes later when Cunningham's long clearance up field sent Forssell clear on goal.
The linesman's flag stayed down and the Blues striker closed in on goal from just inside the Leeds half before slotting the ball across the Leeds' goalkeeper.
Birmingham rounded off a successful afternoon when Forssell converted from the penalty spot 10 minutes from time.
The spot kick had been awarded after Dominic Matteo was adjudged to have pushed Morrison.
Birmingham: Maik Taylor, Martin Taylor, Upson, Cunningham,
Grainger, Johnson, Hughes, Clemence, Lazaridis,
Forssell (John 83), Morrison (Tebily 84). Subs not used: Bennett, Cisse, Carter.
Leeds: Robinson, Kelly, Caldwell, Matteo, Domi, Pennant,
McPhail, Seth Johnson, Milner (Simon Johnson 78), Viduka, Smith.
Subs not used: Carson, Harte, Radebe, Keegan.
Referee: M Halsey (Lancashire).