A whirlwind start set up Manchester City for a win that piles the pressure on Birmingham boss Steve Bruce.
David Sommeil scored on 42 seconds and Joey Barton's penalty made it 2-0 after Nico Vaesen fouled Darius Vassell.
Antoine Sibierski powered home a header from Barton's free-kick to make it 3-0 before Bradley Wright-Phillips wrapped up City's win with a superb strike.
Birmingham managed a late consolation through Jiri Jarosik before Vaesen was sent off for his second booking.
With top scorer Andy Cole suspended it was anticipated that City boss Stuart Pearce would struggle to replace him up front.
But nothing could have been further than the truth, as Sibierski's aerial power - combined with Vassell's pace - proved too much for Birmingham to handle.
City went close even before Sommeil's early goal when Vassell brought a super save from Vaesen after latching on to Sibierski's downward header and bursting clear.
From the resultant corner the pair linked up again - the ball falling for Sommeil to smash home from close range.
More chances followed in quick succession - Vassell failing to finish when Nicky Butt's back-header landed at his feet, and Sibierski's drive hitting the post.
So it was no surprise when City did score a second on 14 minutes - Vaesen up-ending Vassell in the box and Joey Barton slotting home the resultant penalty.
Birmingham reshuffled soon after - bringing on Mikael Forssell to partner Walter Pandiani up front and switching to a 4-4-2 formation, then attempting to add some pace to their line-up by introducing Jermaine Pennant.
Those changes did stem the tide, but City continued to look dangerous and all but wrapped up their win on 40 minutes.
Sibierski beat Vaesen to Joey Barton's free-kick and headed home to make it 3-0 - underlining the home side's complete superiority.
The pattern continued at the start of the second half when a whipped Barton free-kick narrowly evaded Trevor Sinclair, and Barton also sent over an enticing cross which was only just too strong for Vassell.
And there were more goals in the home side too - their fourth coming from substitute Bradley Wright-Phillips on 68 minutes.
Seconds after replacing Vassell, he ran on to Sibierski's cushioned knockdown and steadied himself before firing into the bottom corner.
With manager Stuart Pearce roaring them on from the touchline there was no danger of City taking their foot off the pedal in the closing stages.
Yet Birmingham were still able to salvage some pride when Jarosik found the net with a low finish for a goal that was nothing more than a consolation.
However, there was still time for Vaesen's day to get even worse at the end of the 90 minutes.
He was penalised for handling outside the area, and having been booked when conceding the earlier penalty, his second yellow card meant an early bath.
It was left to midfielder Stephen Clemence, son of legendary England keeper Ray, to replace him between the sticks - but he did not get a chance to show whether he has inherited his father's shot-stopping prowess.
Manchester City manager Stuart Pearce:
"We told the players that they needed to lift their tempo - and to be fair, they delivered.
"I was pleased for them, there were some good performances there.
"But we still have to improve our passing. I never feel completely secure even at three or four up and we need to get more streetwise."
Birmingham boss Steve Bruce:
"It was a total pasting. To say I am hugely disappointed is an understatement.
"We pride ourselves on organisation and team spirit at this club but all that has evaporated here. We were totally and utterly pathetic.
"It was a humiliation. As manager you take overall responsibility - but it is about time some of our players stood up to be counted."
Man City: James, Sommeil, Onuoha, Distin, Thatcher, Sinclair, Barton, Reyna (Fowler 71), Jihai, Sibierski (Ireland 84), Vassell (Wright-Phillips 68).
Subs Not Used: Croft, Jordan.
Booked: Sinclair, Jihai.
Goals: Sommeil 1, Barton 15 pen, Sibierski 40, Wright-Phillips 70.
Birmingham: Vaesen, Tebily (Forssell 23), Upson, Cunningham, Painter, Johnson, Butt, Clemence, Clapham, Pandiani (Jarosik 73), Dunn (Pennant 35).
Subs Not Used: Maik Taylor, Heskey.
Sent Off: Vaesen (90).
Booked: Vaesen, Clemence.
Goals: Jarosik 76.
Ref: S Bennett (Kent).