The Whites comprehensively failed to hit the heights of a number of their exhilarating performances thus far this season, with a first-half double from Che Adams helping to inflict a first home league defeat upon the Whites since March 7.
A late strike from Gianni Alioski provided late hope for United, in a stop-start second half in which referee Peter Bankes struggled to retain control, but the hosts could not forge a leveller.
After some dazzling play on Tuesday night, few would have foreseen the events of the first half when Leeds were second best to a tactically astute and strong Birmingham side - and deservedly trailed at the interval.
Blues hassled and harried the hosts incessantly and produced some accomplishment in the final third, particularly down United's right.
Going forward, Leeds were sloppy, so much so that Marcelo Bielsa - after making a first-half tactical change in the trip to Swansea last month - repeated that action, with Kalvin Phillips again being the player to make way.
It yielded a touch of improvement ahead of the half-time, but it was still a half of dissatisfaction for the leaders.
Blues, unlucky to only draw in midweek at Sheffield United, were afforded the perfect early fillip after catching United napping seven minutes in.
A quickly taken free-kick from Kristian Pedersen, who had a strong first half, found Adams and the ex-Blade's swerving strike from distance seemed to wrong-foot Bailey Peacock-Farrell before nestling into the back of the net.
The jolt failed to pep up Leeds, who failed to get their customary passing game together, with Blues firmly in the faces of those in white.
Just before the break, Blues also made capital from another foray down the left, with Pedersen winning the ball near the half-way line and finding Jacques Maghoma, who cut inside before supplying Adams, who let the ball roll before unleashing a pinpoint angled low shot which went in off the post.
It was another stunner for Leeds, with Phillips soon making way.
His replacement Stuart Dallas soon produced a rare moment of home quality not in keeping with a poor first half with his excellent cross finding the unmarked Tyler Roberts, but his glancing header lacked direction.
At the other end, Blues went close to a third when Maghoma's shot was blocked before Alioski, one of several home players to have a tough first half, then blazed over to rather sum up United's opening 45 minutes.
Roberts then agonisingly just failed to get on the end of Liam Cooper's header across goal from Alioski's corner.
Switching to a 3-3-1-3 formation, Leeds pieced a decent chance early in the second half, but the alert Harlee Dean superbly blocked Roberts' goalbound shot.
Play soon being decidedly scrappy, with the visitors clearly not averse to a bit of time-wasting with referee Bankes' failure to deal with a number of stoppages incurring the wrath of the home supporters, who directed their fury in the direction of the Merseyside official.
It reached a crescendo when Samuel Saiz was booked with a member of United's backroom staff also cautioned as tempers became increasingly heated.
It had the effect of taking the flow out of the game, with Leeds's best chance coming when substitute Adam Forshaw's crisp volley was straight at Lee Camp following an Alioski corner.
Leeds went close to pulling one back in the final quarter, when Dallas's deflected shot flashed just wide.
A lifeline then arrived when Alioski latched onto a high ball from Saiz and expertly fired home five minutes from time.
A minimum of eight minutes of added time was indicated by the fourth official, with Leeds going desperately to salvaging something from a rough afternoon when Dallas' shot yielded a fine one-handed save from Camp.
Leeds United: Peacock-Farrell; Ayling, Jansson, Cooper, Douglas (Edmondson 71); Phillips (Dallas 34); Harrison, Klich, Saiz, Alioski; T Roberts. Substitutes unused: Blackman, Forshaw, Pearce, Baker, Shackleton.
Birmingham City: Camp,; Collin, Morrison, Dean, Pedersen; Jota (Harding 88), G Gardner (Kieftenbeld 58), Lakin, Maghoma; Adams; Jutkiewicz (Bogle 81). Subs: Trueman, M Roberts, Mahoney, Solomon-Otabor.
Referee: P Bankes (Merseyside).