A beautiful Franck Queudrue strike gave Middlesbrough their third successive win and sent Birmingham back to earth after their derby win over Aston Villa.
Queudrue's 29th-minute strike made the difference in a match played at a cracking tempo, with few clear-cut chances but several bookings.
On 29 minutes, Birmingham defender Darren Purse fouled Szilard Nemeth, and Queudrue curled the resultant free-kick inside Nico Vaesen's near post from 25 yards out.
The effort was a beauty, although there were question marks about Vaesen's positioning.
It was the second time in three minutes that Boro had put the ball in the Birmingham net from a free-kick, but the first effort, touched in by Job from a Geremi sizzler, was ruled out for offside.
Indeed, given the fierce spirit the game was played in, it was no surprise that Birmingham's best chance also came from a dead ball.
On 17 minutes Martin Grainger whipped in a free-kick from the right which eluded the Boro defence and Darren Purse was inches from connecting.
But it was one of the few bright spots for Birmingham, who for the first half were mainly reduced to 30-yard efforts from Grainger and Stern John.
At half-time Birmingham manager Steve Bruce made a positive change, bringing on Stan Lazaridis for Grainger.
And within a minute of the restart Birmingham should have equalised.
A great cross from Damien Johnson wide on the right found the head of Clinton Morrison, but the Ireland striker's downward header flashed wide of Schwarzer's right-hand post.
Another header, this time from Darren Purse from a Lazaridis cross, provided the Blues with another good chance to get back on level terms, but it went high over the bar.
And despite these efforts it was Middlesbrough who continued to have the better of the match.
Jonathan Greening had a powerful 25-yard shot well saved by Vaesen, while substitute Alen Boksic also went close.
But Birmingham nearly had the last laugh - literally - late on by taking advantage of a second goalkeeper howler in two games.
With five minutes to go, Jovan Kirovski's mishit shot was fumbled by Boro goalkeeper Mark Schwarzer, but no Blues player was close enough to capitalise on the error.
Middlesbrough: Schwarzer, Ehiogu, Vidmar, Cooper, Stockdale, Greening, Geremi, Queudrue, Job (Wilkshire 76), Nemeth (Boksic 63), Maccarone.
Subs Not Used: Marinelli, Crossley, Whelan.
Booked: Greening, Maccarone, Boksic.
Birmingham: Vaesen, Kenna (Kirovski 81), Purse, Cunningham, Grainger (Lazaridis 45), Devlin, Savage, Cisse, Damien Johnson, John (Horsfield 66), Morrison.
Subs Not Used: Bennett, Powell.
Booked: Morrison, Purse, Savage, Cisse.
Attendance: 29,869.
Referee: A D'Urso (Essex).