Stephen Hunt's second-half penalty earned Reading a 1-1 draw and ruined Alex McLeish's first home match as Birmingham manager.
Hunt scored from the spot after he had been brought down by Blues keeper Maik Taylor following a weak back-pass from Mat Sadler.
That cancelled out Mikael Forssell's strike but City had enough chances to have collected points with Royals keeper Marcus Hahnemann producing some crucial saves and Ibrahima Sonko making a spectacular clearance off the goal-line with the help of the underside of the crossbar.
Blues went ahead on 4 when Gary McSheffrey's corner was flicked across the face of goal by Fabrice Muamba and, although Nicky Shorey blocked Forssell's initial header, the Finnish ace bundled the rebound over the line.
But Hunt levelled on 51 sending the Northern Ireland number one the wrong way from the spot.