Birmingham recorded their fifth straight win as they coasted to a 2-0 victory at Rotherham.
Two goals in eight first-half minutes put the Blues in a commanding position and they never really lost control from there on in.
Chris Davies' side remain level on points with Wrexham at the top of the table
The first goal came when Tomoki Iwata reacted clinically to Jay Stansfield's blocked shot and drilled into the bottom corner from the edge of the box.
Stansfield netted the second himself as he lobbed Dillon Phillips after being picked out expertly by Willum Willumsson.
Birmingham could have added more in the second half, with Lyndon Dykes and Scott Wright both threatening a third.
Alex Cochrane came even closer late on when he rattled the goal frame with a powerful free-kick from the edge of the box.