Had it not been for a superb performance from visiting goalkeeper Nico Vaesen, the Citizens would have triumphed by a bigger margin.
In the end they had to settle for first-half strikes from David Sommeil, Joey Barton and Antoine Sibierski and a late effort from substitute Bradley Wright-Phillips, as the hosts climbed back into seventh place.
Whilst the Mancunians had plenty to cheer, it was an altogether different story for visiting boss Steve Bruce, who will want to forget his side's poor showing.
Darius Vassell almost scored the fastest goal of the season, but was denied by a save from Vaesen after only 12 seconds.
But from the resulting corner right-back Sommeil fired the Citizens ahead with just 44 seconds on the clock. Sibierski headed a Sun Jihai corner towards goal and Vassell laid the pass back for Sommeil to score.
Pearce's men produced some excellent attacking play as Vassell lobbed narrowly wide and Sibierski shot against the upright.
It was no surprise when they doubled their lead after 15 minutes after Vaesen brought down Vassell, who had burst through on goal. The keeper was booked and then had to pick the ball out of the net for a second time as Barton scored from the spot.
Manchester continued to attack relentlessly with the ever dangerous Sibierski forcing Vaesen to make two excellent saves, each time to keep out headers.
Birmingham manager Bruce was made two first-half substitutions, bringing on Mikael Forssell and Jermaine Pennant, but the changes failed to improve Birmingham's fortunes and five minutes before half-time, Sibierski added a richly deserved third.
Sun was tripped by Damien Johnson and the Frenchman beat Vaesen to Barton's free-kick and headed into the empty goal.
The home side were almost as quick out of the blocks at the start of the second period. Within 90 seconds of the restart Vaesen had made excellent saves to deny Vassell and Barton.
Perhaps it was inevitable that they could not maintain the intensity of the first half, but they still managed to score a fourth as Wright-Phillips found the net a little over a minute after make his entrance as a substitute.
The 20-year-old got onto the end of a Sibierski knock down and found the net with a sweetly-struck shot from the edge of the area.
Birmingham grabbed a 76th-minute consolation when substitute Jiri Jarosik cut in from the right and drilled a shot low past David James.
However, the visitors' misery was completed in stoppage-time when Vaesen, booked earlier for conceding the penalty, was sent off for handling the ball outside the area.
Man of the Match: Antoine Sibierski
The Frenchman was involved in most of the hosts' attacking play in what was his first start for almost two months.