Lee Johnson watched from the stands as his promotion-chasing Bristol City lost ground with a 2-1 Championship defeat by Birmingham at Ashton Gate.
The head coach was serving a touchline ban after picking up his fourth yellow card of the season at Norwich on Saturday.
Birmingham looked the sharper side in the first half and went ahead in the 42nd minute when Connor Mahoney cut in from the left and saw his low right-footed shot deflected past Niki Maenpaa.
Two minutes after the break, Garry Monk's side doubled their advantage, centre-back Michael Morrison rising unmarked to nod home a Mahoney free-kick.
Famara Diedhiou put Bristol back in the game in the 66th minute with a simple tap-in from Matty Taylor's header across goal.
But, despite dominating from then on, the hosts could not force an equaliser and Birmingham moved menacingly to the fringe of the play-off race.
Both sides went close in the early stages. Bristol's Andreas Weimann saw a low shot from the edge of the box pass inches wide after latching onto Adam Webster's pass.
From the resulting 12th-minute corner, Birmingham produced a lightning break that ended with Mahoney crossing from the left and Kerim Mrabti seeing his well-struck shot brilliantly saved by Maenpaa.
The visitors went close again moments later with another raid out of defence. Che Adams let fly from 25 yards and his effort bounced down off the crossbar before being cleared.
Birmingham were looking as bright and Mahoney was next to test Maenpaa with a shot from distance, comfortably gathered by the Bristol 'keeper.
Bristol came up with a telling break of their own in the 29th minute, Weimann drilling a pass to Diedhiou inside the box and the big striker shooting over when he should have scored.
Mahoney's goal followed a lull in the action, but was no more than they deserved. Marlon Pack's poor touch inside his own box allowed the opportunity to develop and Maenpaa was given no chance by the deflection.
Johnson made two changes for the second half, sending on striker Taylor and winger Niclas Eliasson. But before he knew it poor defending had gifted Morrison Blues' second goal.
It was almost 3-0 on the hour when Adams broke into the box and rounded Maenpaa, only for his shot to be blocked on the line by Tomas Kalas.
A third Bristol substitute, Jamie Paterson, provided the cross, which Taylor nodded down for Diedhiou to score and with 24 minutes left, Johnson's men were back in the game.
The home side piled on the pressure, but most of their goal attempts came from distance as Birmingham defended strongly to clinch the points.
The managers
Lee Johnson: "It was a tough watch from up there. Birmingham came with a game plan and we were not good enough tactically or in terms of individual performances to break it down. The first half was really disappointing and we were guilty of poor defending in allowing their goal. The second one after the break came because we had a player blocked off at a free-kick. We knew they did that and had warned the referee and fourth official.
"In the light of that, it was disappointing that they missed the offence. It was a key moment because I thought our substitutes had a positive effect and we were much better in the second half. We are where we are and I felt one or two players looked leggy after the game at Norwich on Saturday. That was one of the reasons I made a couple of changes at half time."
Garry Monk: "We can't control what goes on off the pitch and our season has been all about giving the fans performances they can take pride in. That is happening more and more and we will just see where it takes us. I thought we were magnificent tonight.
"To play like that against the form team of the Championship was fantastic. I know Bristol lost on Saturday, but they have been playing really well."