The hosts broke the deadlock 44 minutes into an evenly-matched first half when Tom Ince’s speculative low drive took a significant deflection off Blues captain Davies.
Birmingham striker Marlon King tried his luck with an overhead kick on 13 minutes before Nathan Redmond thrashed just beyond the bar after Chris Burke found some space down the Blackpool left.
King might have done better when his shot from Burke’s cutback clipped the top of the bar at the end of a clinical 40th-minute counter attack.
It was a miss he lived to regret a minute before the interval when Ince’s 25-yard effort deflected off Davies and squirmed past Doyle.
Chris Hughton’s side were forced onto the back foot in the second half, with former Liverpool youngster Ince forcing Doyle into a scrambling save, while Stephen Dobbie passed up the chance of the night to double the home side’s lead ahead of the return leg on Wednesday.
BLACKPOOL: Gilks, Eardley, Baptiste, Evatt, Crainey, Ferguson, Angel, Dobbie (K Phillips 75), M Phillips, Taylor-Fletcher (Dicko 75), Ince.
BIRMINGHAM: Doyle, Ramage, Davies, Ibanez, Murphy, Burke, N’Daw, Mutch, Elliott, Redmond (Spector 74), King.
Referee: Mark Halsey