Trevor Francis's side have manoeuvred themselves into a position of strength courtesy of a second-half winner from Nicky Eaden that tees-up an intriguing second leg at Deepdale on Thursday night.
But Francis will reflect that if they not had been so profligate throughout a one-sided second half the damage could, perhaps should, have been irreparable.
Instead it is inconceivable that Preston, having offered next to nothing in the way of attack-minded football, will be so pallid on their ground.
In the first half, in particular, Birmingham lacked any kind of width or penetration to test their opponents.
After the break, however, Stan Lazaridis became a more potent threat on the left and Birmingham's greater sense of adventure was rewarded in the 55th minute. Peter Atherton lifted a free-kick into the penalty area which Marcelo, with his back to goal, brought under control and attempted a shot despite the proximity of several defenders. The ball ricocheted into Eaden's path and his right-foot drive from 12 yards was still rising as it hit the back of David Lucas's net.
Few places have better acoustics than St Andrews in full voice and the old stadium reverberated to the sound of Brummie celebrations that, if Geoff Horsfield and Marcelo had not subsequently squandered close-range opportunities, would have been even more raucous by the final whistle.
Birmingham: Bennett, Atherton, Purse, Michael Johnson, Woodhouse (Hughes 83), Eaden (McCarthy 86), O'Connor (Holdsworth 80), Sonner, Lazaridis, Horsfield, Marcelo. Subs Not Used: Poole, Gill. Booked: O'Connor. Goals: Eaden 55.
Preston: Lucas, Alexander, Murdock, Kidd, Edwards, Cartwright, Gregan, McKenna, Cresswell, Macken (Anderson 81), Healy. Subs Not Used: Moilanen, Barry-Murphy, Collins, Gunnlaugsson. Booked: Gregan, Cresswell, Kidd, Alexander.
Referee: D Pugh (Bebington).