It's a massive win on the road for José Morais' men as Barnsley ease to a convincing victory over Blues at St Andrew's.
A first half double from Oli McBurnie was enough to see the Reds to a priceless three points in this relegation battle.
The on-loan striker gave Barnsley the lead when he hooked a clever volley past David Stockdale on 12 minutes, before seeing a penalty saved by the 'keeper and then notching his second of the afternoon when he stabbed the ball home from close range.
José Morais had made five changes to the side that lost on Tuesday night against Burton Albion at Oakwell; starts for Mamadou Thiam and Kieffer Moore up front with Brad Potts back in midfield. Welcome returns in defence for Zeki Fryers and Adam Jackson after lengthy spells out injured.
After an opening five minutes where both sides looked to win the midfield battleground, it was the Reds who won out, with Gary Gardner and Joe Williams taking the game by the scruff of the neck, allowing Brad Potts to marauder forward at will.
And it was Potts' clever heel flick that saw Fryers fire in a first-time effort from 25-yards out that whistled narrowly over the Blues crossbar on eight minutes.
On the counter attack, Nick Townsend had to be at his very best when he somehow twice denied Jeremie Boga from inside the six-yard box.
And after a dozen minutes played, the pressure paid off with McBurnie's first...
It was wonderful link-up play by Potts and captain Andy Yiadom on the right side, Thiam burst into space, cut back onto his left foot and his low cross was hooked into the far corner by McBurnie on the volley to send the away fans into raptures.
It could have been 2-0 when Yiadom's right footed cross was met sweetly by Moore, but his goalbound shot was blocked by Marc Roberts, Potts seized upon the loose ball and layed it off perfectly for McBurnie whose shot was timid and easily kept out by Stockdale.
However, on 17 minutes McBurnie would get another opportunity when he was bundled over by Roberts in the box, a Reds penalty...
But the Scottish hitman's fierce spot kick was superbly kept out by the 'keeper, low to his left.
It was 2-0 though on 35 minutes when another Thiam cross, this time right-footed was headed back across goal by Moore and there was McBurnie to get a toe to the ball ahead of the 'keeper and stab the ball home.
Gary Gardner nearly added a third towards the break, but his curled effort whipped just over the crossbar.
Roberts had the ball in the back of the Reds net after Townsend had initially denied Boga, but the former Barnsley man was in an offside position.
HALF TIME: Birmingham City 0-2 Barnsley
The Reds were in control as the game re-commenced after the interval, keeping Blues at bay and still creating breaks forward.
Connor Mahoney came on for the impressive Thiam with an hour played.
After Moore saw his header deflected wide for a Reds corner, Mahoney swung in the set-piece and Moore this time got lots of power on his header only to see it drop just wide of the far post.
Birmingham's best chance came on 66 minutes when Sam Gallagher closed down Townsend's clearance, the ball ricocheted nicely for the big striker who squared for Che Adams who looked nailed on to score, but an excellent sliding block by Liam Lindsay thwarted Blues.
Christoph Knasmüllner made his Barnsley debut on 77 minutes, replacing goalscoring hero McBurnie.
Matty Pearson came on for the outstanding Gardner with five minutes left on the clock.
And the Reds saw the game out with ease really, with Mahoney drilling an effort just wide the highlight of the closing stages, as Barnsley recorded a league double over Blues and earned a huge three points ahead of another tough trip on Tuesday night as Morais' men head to Hull.
FULL TIME: Birmingham City 0-2 Barnsley
Reds: Townsend (GK); Yiadom, Jackson, Lindsay, Fryers; Gardner (Pearson 85), Potts, Williams; McBurnie (Knasmüllner 77), Moore, Thiam (Mahoney 60).
Unused: Davies (GK), Cavaré, Moncur, Bradshaw.