Substitute Jay Denny was League Two Shrewsbury's two-goal hero as they dumped Brighton out after extra-time.
Mark McCammon's spectacular header from Sebastien Carole's cross put the Seagulls ahead before Jamie Tolley set up Mark Stallard to equalise.
Brighton looked to have booked their second-round place when substitute Jake Robinson swept home McCammon's cross.
But American Denny sent the tie into the extra period before converting Colin McMenamin's right-wing cross.
Shrewsbury: Hart, Herd, Walton, Hope, Sharp, Tolley (Denny 45), Sorvel, Hogg (Ashton 88), Smith, McMenamin, Stallard (Langmead 96).
Subs Not Used: Lyng, Thompson.
Goals: Stallard 22, Denny 89, 91.
Brighton: Chaigneau, El-Abd, Butters, McShane, Reid, Carole (Jarrett 68), Nicolas, Hammond, Knight, McCammon, Kazim-Richards (Robinson 52), Jarrett (Carpenter 87).
Subs Not Used: Hart, Martin.
Booked: Nicolas, Robinson.
Goals: McCammon 17, Robinson 80.
After Extra Time.
Ref: T Parkes (W Midlands).