Steve Morison inspired Millwall to a comfortable 2-0 Sky Bet Championship win against a sterile Birmingham side as new manager Steve Cotterill's unbeaten start came to an end at the Den on Saturday evening.
The Blues offered little as an attacking threat in what was a cagey performance, falling behind at the start of the second half when full-back Maxime Colin turned the ball past his own goalkeeper from Morison's cross.
Substitute Tom Elliott made the second with a driving run and shot which drew a smart save from Tomas Kuszczak, with Ryan Tunnicliffe on hand to calmly slot home from the rebound.
Isaac Vassell had wasted Birmingham's best chance on the stroke of half-time, flashing a shot wide of Jordan Archer's post after being played in by Che Adams as Cotterill's strugglers made it one win in 13 Championship games this season.
Cotterill had seen his new side win against high-flying Cardiff last Friday but it was clear that the bubble had burst early-on in south London, with Birmingham seemingly reluctant to take the game to their mid-table opponents.
Andy O'Brien volleyed over for Millwall from Jake Cooper's header midway through the first half but Neil Harris's side looked content to look long and rely on knock-downs from the lively Morison.
It was a mark of the lack of goalmouth activity that Che Adams' wicked ball across goal ten minutes before half time was one of the highlights of the first 45 minutes, with no one in the white of Birmingham having gambled on what would have been an easy tap-in.
Vassell slipped his low shot past the post with Archer beaten as half time approached and Blues were made to pay in the first minute of the second half when Morison crossed for the hapless Colin to slide the ball past Kuszczak with O'Brien lurking.
Birmingham briefly rallied with Adams shooting straight at Archer from 18 yards but the game was put beyond them when Elliott, on for the superb Morison, got on the end of Lee Gregory's through ball and cut inside to shoot at goal, only for Kuszczak to parry into the path of the grateful Tunnicliffe who finished well.
It was no more than Millwall deserved as they disposed of a lacklustre Birmingham, who sit precariously placed one point above the relegation zone ahead of the first Midlands derby of the season against Aston Villa next weekend.
The managers
Neil Harris: "Birmingham came to compete and I thought we put in an outstanding Millwall performance. Despite the odd spell, we were on the front foot for the whole game.
"I said to my players before the game that as much as it will be a fight, a scrap and a battle - and all about second balls - I also knew that there'd be opportunities for moments of quality during the game. I thought we had the key moments, especially in the play leading up to the goals."
Steve Cotterill: "I didn't think that because we won last week that we'd cracked it. We know we're going to have put performances in back to back. This game was important in terms of building on last week's result. We've made it doubly difficult for ourselves by not winning; it doesn't help us put confidence back into the team."
Man of the match - Steve Morison
Morison was the fulcrum of Millwall's attacking plan, using his body well to out-muscle the Birmingham defence and win his share of knock-downs in the first half, before his probing cross forced the error which led to the opening goal.
What's next?
Birmingham host Aston Villa in the Midland derby next Sunday at 12.00pm whilst Millwall travel to Cardiff on Saturday at 3.00pm.