Alex Cochrane scored inside a minute as Birmingham buried Millwall with a first-half goal rush to earn a 3-0 win in the Championship at St. Andrew's.
Cochrane, Max Bird and Jay Stansfield netted with left-footed finishes before half-time to ease the loss of seven-goal striker August Priske with a knee problem.
It put City on their way to their sixth win in eight and extended their unbeaten Championship home start to seven games.
Cochrane netted when he lashed home a loose ball from 30 yards when Millwall failed to clear a long pass and Phil Neumann's shot hit a defender. Goalkeeper Max Crocombe was motionless on his line as Cochrane netted for the second successive game.
Millwall forced City goalkeeper Ryan Allsop into a flying save from Caleb Taylor's glancing header following a long throw and Kyrell Lisbie hooked over from the rebound.
City made the visitors pay by doubling their lead in the 16th minute. Bird steered home a left-footed drive from 15 yards after sidestepping Derek Mazou-Sacko before taking on Taylor to celebrate his first start for Birmingham.
Blues continued to threaten and Stansfield's curling shot was palmed away by Crocombe before Jhon Solis' downward header bounced straight at the Millwall goalkeeper.
But in between Millwall wasted the opportunity to reduce the arrears when former City striker Lyndon Dykes flashed a rising drive over the bar as he fell. Jake Cooper then scooped a similar effort over from Lisbie's low cross.
Blues made them pay by making it 3-0 with a fine breakaway goal in the 29th minute. Stansfield took Bird's pass and ran at the defence before cutting inside Cooper and sending a left-footed drive through Taylor's legs into the bottom corner from just outside the box.
The home side continued to hold the upper hand following the restart, although it was Millwall who showed first. Cooper fired straight at Allsop but Crocombe remained the busier of the two keepers.
Crocombe had to dive to his right to keep out Stansfield's shot on the turn from the edge of the box and then he smothered another Stansfield effort and Patrick Roberts's curling shot.
Millwall's closest effort was a thunderous shot from Camiel Neghli that shook the crossbar in the 75th minute.
Substitute Carlos Vicente went within a whisker of making it 4-0 when his angled shot came off the inside of a post and rolled back to Crocombe.
Birmingham's Chris Davies:
"We are in a position we deserve to be in. Sometimes you go into a false position and we snuck in.
"But we have earned it with our performances and the way the team looks. We've got to enjoy it and take belief and confidence from it. We have made good strides so far.
"It was a big win against a very good opponent. We made a perfect start scoring inside the first minute.
"I wanted us to continue with the same fight, organisation and physicality and with the ball try to be as fluid as we could and there was a lot to like in the first half."
Millwall's Alex Neil:
"We conceded in the first minute, then we had an opportunity to equalise but Kyrell Lisbie put it over the bar. We went gung-ho looking for an equaliser and got hit by a sucker punch.
"They broke up the pitch and scored from outside the box and then we got another opportunity to score and didn't take it. They then broke again and scored the third goal. The game was done at 3-0.
"I thought it wasn't just a case of 'we missed, they scored' but after the first goal, we lacked discipline in the middle of the pitch. The space in front of the two centre-backs was too vacant.
"We needed to be more clinical in the final third, stop the transition and, in two-versus-one situations, make the extra man count."
