Blues forward Scott Hogan scored the only goal of the game in the 26th minute as former Boro boss Aitor Karanka claimed a win over his former club.
Our Boro writer Joe Nicholson has dished out his marks from the match– scroll down and flick through the pages of our picture gallery to see how each player fared:
9. Marvin Johnson - 5
Failed to track Maxime Colin for Birmingham’s opener as Boro were exposed on the flank in the first half. Withdrawn after the break. 5 Photo: George Wood
10. Lewis Wing - 5
Struggled to make an impact in after starting in an advanced midfield role. Subbed off at the break. 5 Photo: Laurence Griffiths
11. Chuba Akpom - 5
Hardly had a kick as Birmingham’s centre-backs dominated in the air in the first half. Was also taken off at the break. 5 Photo: Getty Images
12. Britt Assombalonga - 5
(for Akpom, 45) Looked lively when he came on but faded. 5 Photo: Getty Images