Birmingham remain in relegation trouble in the Championship after Millwall claimed a third consecutive win with a 2-0 victory at The Den.
An early Jed Wallace goal put the hosts in the ascendancy and Ben Thompson's tap-in after 75 minutes made sure of the three points as Millwall continued to climb the table.
The hosts could not believe their luck, when after just over two minutes, a Birmingham mix-up allowed Wallace to beat Neil Etheridge off his goal line and poke the ball into an empty net.
It would have been easy for Blues, who came into the game above only Wycombe in the table, to lose faith after that but Aitor Karanka's side steadied the ship and shared possession with the Lions for the opening exchanges.
Skipper Harlee Dean had a chance to level things up after 12 minutes when a corner dropped to him but he lashed it wide via a deflection.
Millwall boss Gary Rowett will have been disappointed to see Jake Cooper leave the field with a shoulder injury after just 22 minutes as he was replaced by Alex Pearce.
Moments later Matt Smith got on the end of a Mahlon Romeo cross but could not direct his powerful header on target.
Blues' best chance to level things up before the break fell to Dean after Bartosz Bialkowski completely miscued his punch but once again his effort sailed high and wide.
The Lions should have doubled their lead in the 56th minute when Smith broke the line and squared for Mason Bennett, but Scott Malone got their first and forced the save from Etheridge and when Smith looked certain to tap in the follow-up, Dean was there to make a vital block.
Birmingham eventually forced their first shot on target when Lukas Jutkiewicz stung the palm of Bialkowski before a handball by the striker brought the attack to a premature end.
But Rowett's side killed the game after 75 minutes when centre-back Shaun Hutchinson broke free down the right flank and sent a perfect cross into the path of Thompson to finish from point-blank range.
Jonathan Leko did eventually get the ball over the line for Blues in added time but he was ruled offside as Karanka's men remain in 23rd, one point from safety, after a third consecutive loss.
What the managers said...
Millwall's Gary Rowett: "I thought it was a poor performance in certain ways for most of the game. I think a marker was laid down in the first 30 seconds when the Birmingham central defender smashed it 100 yards back to us and it didn't get much better than that. I thought that when we got into the final third, Birmingham would be nervous. The goal comes from the defender under-hitting a backpass, Jed gambles and that is the sort of thing that happens to you when you're down there and haven't won many games.
"So it was a good start for us but I thought after that Birmingham were better than us. We didn't pass the ball with any fluidity and that meant we couldn't get out and attack like we wanted to. We've won four and drawn three now against some excellent sides, Norwich City and Watford included, and the players have shown what they are all about with a really good run of results."
Birmingham's Aitor Karanka: "I don't need to look at the table because it is just a reflection of your job on the pitch. Why am I going to look at the table if we are not winning games. We have to look at ourselves, our work and to keep believing because we have been really good this season. The only way I know is to keep working - to go to the training ground tomorrow and start preparing for the next game.
"One little mistake has cost us a lot tonight because of the position we are in at the moment, to concede a goal like that after two minutes is difficult to take. In a normal situation after that it would look like a team was going to go down but we were really good and we were in the game but we didn't defend well. Last week I said I wasn't happy with the performance but today I can't say anything bad because the players were fighting until the final whistle."