Birmingham boosted their survival hopes and dented Rotherham's as a late winner from Harlee Dean secured a 1-0 win at the New York Stadium on Sunday.
Rotherham carved out decent opportunities for themselves throughout the 90 minutes, despite the Blues' visit being their fourth game since last Saturday, but failed to take them and were punished late on as a result.
Two minutes from time, a cross from the left flank was helped to the far post by Kristian Pedersen, where Dean leapt to meet it with company from Michael Ihiekwe.
Although Dean was initially credited with the goal, replays suggested it may later be confirmed as an own goal, with Ihiekwe's touch appearing to take the ball over the line.
A third win in four matches for Lee Bowyer's men - coupled with a fourth straight clean sheet - moves them nine points clear of the relegation zone, while Rotherham remain in 22nd, albeit with two games in hand over many of the teams around them.
Clearly sensing a chance to prey upon a Rotherham side in the midst of an even more congested schedule than usual, Birmingham charged forward from the off, with Lukas Jutkiewicz heading Maxime Colin's cross over the bar inside the first 20 seconds.
They then tried to utilise Marc Roberts' long throw, with little success, before Steve Seddon sent a ball skidding across the six-yard box, with a well-placed Jonathan Leko unable to apply the telling touch from a central position.
oth sides had penalty claims waved away by referee Tim Robinson, too. The hosts were denied when the ball appeared to strike Pedersen's arm as he controlled a ball forward and, not long after that, the Blues had appeals turned down when Seddon was caught in the area.
The Millers grew into the game and passed up two opportunities midway through the first half. Angus MacDonald's faint touch on Lewis Wing's cross sent the ball beyond the far post, while Michael Smith could only loop a shot wide after being picked out by Matt Crooks.
They started the second half in a similar fashion. Freddie Ladapo had a shot cleared by Gary Gardner after Birmingham goalkeeper Neil Etheridge struggled to claim a corner from the left, before Richard Wood squared for the unmarked Wing, whose shot was blocked by Pedersen.
Inside the final 15 minutes, Jutkiewicz forced a smart save from Viktor Johansson after meeting another cross from Colin and then just as it looked as though the Millers would collect a valuable point, Dean headed in to send all three points back to St Andrew's.