In their final game before the Championship campaign kicks off, Birmingham had two summer signings to thank for a confidence-boosting victory.
Blues took the lead after 12 minutes thanks to Matt Green, who was left unmarked to head in a Shane Ferguson corner.
They doubled their advantage minutes after the restart after James Chester was caught in possession by Scott Allan, who left Andrew Shinnie with a tap-in.
Former Birmingham manager Steve Bruce did have something to shout about after 75 minutes when Paul Robinson brought down Sone Aluko in the area.
Birmingham Academy graduate Aluko took the penalty himself, sending Darren Randolph the wrong way, but Blues held on.