Carlos Tevez scored the only goal as Manchester United secured a narrow victory to stay two points behind Premier League leaders Arsenal.
Carlos Tevez celebrates his ninth United goal in unorthodox fashion
Tevez's overhead kick and a Cristiano Ronaldo back-heel carved open the Blues defence and the Argentine calmly slotted home the winner on 25 minutes.
Cameron Jerome was down injured then but Birmingham complaints were limited.
Tevez, who went off late on with an ankle injury, also hit the woodwork twice while the Blues never gave up.
United manager Sir Alex Ferguson, sat in the stands to serve out his two-match touchline ban, made five changes to his starting line-up.
Ronaldo partnered Tevez in the centre of attack with Wayne Rooney still absent with a virus and Ryan Giggs not even on the bench.
Birmingham boss Alex McLeish - once a protege of Ferguson in their days together at Aberdeen - started with two up front.
Jerome, partnering Gary O'Connor, heeded the positive mantra of his boss and scorched a long-range effort over Tomasz Kuszczak's bar within 60 seconds.
But Ronaldo soon set about making amends for his penalty miss in the defeat against West Ham on Saturday.
After five minutes, he smuggled the ball through to the onrushing Patrice Evra who whipped the ball across the box from the left for Tevez to head against the foot of Maik Taylor's post from three yards.
With Birmingham's midfield struggling to win possession, United's creative players bossed the tempo.
The inevitable goal came when Tevez dropped deep to flip a pass over his head for Ronaldo, who controlled the ball and instantly back-heeled it into the path of the Argentine.
Tevez, having pulled Liam Ridgewell and Rahdi Jaidi out of position, marched into the space and clinically passed the ball past Taylor into the corner of the goal.
It was his eighth league goal this season and he celebrated in bizarre style - sucking on a pink baby's dummy.
But 15th-placed Birmingham fought to find their way back into the game and, helped by the jitters of United's defence, carved out a couple of opportunities.
Birmingham fought hard against a below-par Manchester United
A Rio Ferdinand error and Fabrice Muamba's clever switch of play twice gave Gary McSheffrey time and space around the United box, yet he blazed shots high and wide.
No personnel changes were made at half-time and neither did the pattern of play alter.
Making his first United start since March, South Korea international Park Ji-sung raced to the byeline on 55 minutes to deliver a wicked cross onto the head of a leaping Ronaldo.
The Portuguese headed downwards powerfully but a superb reaction stop from the feet of Taylor kept the ball out and Birmingham in the game.
Minutes later Tevez crashed a shot against the post and a posse of Birmingham defenders bravely kept out Ronaldo's follow-up attempt.
The one-way traffic continued with Tevez and Ronaldo orchestrating a 15-minute onslaught.
Yet Birmingham brought on Mikael Forsell for Jerome and he swiftly helped remind United of the slenderness of their advantage as City enjoyed their best spell.
First, he worked space for O'Connor to place a decent effort on target, before shooting hard and low himself without success.
With minutes remaining, Forsell found space but scuffed a shot wide with team-mates better placed to his right before United played the clock down for an important victory.
Manchester United defender Rio Ferdinand:
"It was good to get back to winning ways and take the three points. I'm pleased with the clean sheet after we gave away two sloppy goals against West Ham.
"It is disappointing not to get more goals, but it's the win that counts.
"We weren't nervous at the end and we know in certain games we have to defend 1-0 leads.
"It doesn't matter what Arsenal do. It we continue grinding out results then we know we have the players who can do the damage up front."
Birmingham manager Alex McLeish:
"They looked as if they would score every time they went up the pitch but I really felt we could nick something.
"We had a really good start to the game and got into a number of good positions but just couldn't hit the target.
"The United fans whistling for the final whistle was like music to my ears but we just couldn't make the breakthrough.
"If we can add two or three players in the transfer window to help the players then that will be fantastic. The players know it's not a threat to them."
Man Utd: Kuszczak, O'Shea, Ferdinand, Vidic, Evra (Brown 84), Ronaldo, Anderson, Carrick, Nani, Park (Hargreaves 75), Tevez (Saha 71).
Subs Not Used: Heaton, Pique.
Goals: Tevez 25.
Birmingham: Maik Taylor, Kelly, Jaidi, Ridgewell, Queudrue, McSheffrey (De Ridder 67), Nafti (Palacios 81), Muamba, Larsson, Jerome (Forssell 67), O'Connor.
Subs Not Used: Doyle, Parnaby.
Booked: Ridgewell, Queudrue, Nafti, Palacios.
Ref: Peter Walton (Northamptonshire).
BBC Sport Player Rater man of the match: Manchester United's Carlos Tevez 8.15
Please note that you can still give the players marks out of 10 on BBC Sport's Player Rater after the match has finished.