Daniel Nardiello's sensational strike breathed new life into Barnsley's Coca-Cola Championship survival hopes and dealt a serious blow to Birmingham's automatic promotion bid.
The former Manchester United trainee's brilliant individual effort in the 52nd minute settled the match but Birmingham boss Steve Bruce will wonder how his side ended up without a point.
They battered Barnsley without reward in the second half, hitting the post, having several shots cleared off the line and also seeing strong penalty claims ignored by referee Mike Russell.
Once again, however, Birmingham's lack of a cutting edge proved their undoing as DJ Campbell, Cameron Jerome and Nicklas Bendtner all faltered in front of goal to leave 7,000 travelling supporters bitterly disappointed.
After a dismal 1-0 home defeat against Burnley on Saturday, this latest setback was further proof that Steve Bruce's men are losing their nerve when it matters most.
Ugly scenes erupted at the final whistle as Blues midfielder Neil Danns and Barnsley defender Bobby Hassell were shown red cards fr violent conduct.
Bruce was again denied the services of on-loan Portsmouth striker Andy Cole, who is still nursing a hamstring strain and has yet to make his debut.
Cole watched from the stands but it was another Old Trafford reject in Nardiello who assumed centre stage after just 23 seconds.
The livewire striker found the time and space to fire in a low shot which drew a smart stop from Birmingham goalkeeper Colin Doyle.
Birmingham midfielder Fabrice Muamba, recalled to the side in one of four changes made by Bruce, found Campbell and his low cross found Jerome.
He shot weakly wide from 10 yards and his effort was indicative of Birmingham's impotence in front of goal.
Barnsley took encouragement from Birmingham's failings and they created the best opportunity of the half moments before the break.
Nardiello whipped in a vicious inswinging cross from the right and Martin Devaney's diving header drew a smart stop from goalkeeper Colin Doyle.
Barnsley struck seven minutes after the break when Nardiello collected possession down the left flank and advanced towards goal.
He rode the challenge of several Birmingham players and struck a delightful diagonal low shot across Doyle and into the far corner off the post.
It was his fifth and most important goal of the season and prompted a mini-pitch invasion from Barnsley supporters.
Birmingham dominated the remainder of the game and Barnsley defender Antony Kay looked to have felled Campbell inside the home penalty area.
Vine then stabbed a low cross from McSheffrey wide and Stephen Kelly headed over a McSheffrey corner.
Martin Taylor then did likewise from another McSheffrey cross before substitute Bendtner hit a low shot against the post before Barnsley scrambled the ball clear.
Barnsley (0) 1 Birmingham (0) 0
Barnsley Colgan, Hassell, Kay, Nyatanga,Eckersley (Heckingbottom 36), Devaney (McCann 76), Togwell,Howard, Kyel Reid, Nardiello (Rajczi 84), Ferenczi.
Subs Not Used: Lucas, Jones.
Booked: Togwell.
Goals: Nardiello 52.
Birmingham Doyle, Kelly, N'Gotty (Gray 75), Jaidi,Martin Taylor, Vine (Bendtner 59), Johnson (Danns 71), Muamba,McSheffrey, Campbell, Jerome.
Subs Not Used: Maik Taylor, Nafti.
Att: 15,857
Ref: C Foy (Merseyside).