Blackpool condemned Brighton to their fifth straight defeat and moved above them at the bottom of League One.
The visitors took the lead when Keith Southern made a great run into the area to head home Shaun Barker's cross.
Scott Vernon made it 2-0, reacting quickly to find the net when Ben Burgess headed a corner goalwards.
Brighton had Alexandre Frutos sent off for an alleged elbow on Barker and the Seagulls' misery was completed by Vernon's close-range finish late on.
Brighton: Kuipers, Lynch (Frutos 45), El-Abd, Butters (Hart 77), Whing, Mayo, Hammond, Carpenter (Adam Hinshelwood 62), Cox, Revell, Williams.
Subs Not Used: Sullivan, Gatting.
Sent Off: Frutos (72).
Blackpool: Evans, Coid, Jackson, Barker, Evatt, Southern, Fox, Hoolahan, Gillett (Jorgensen 80), Burgess (Vernon 41), Morrell (Parker 84).
Subs Not Used: Jones, Joseph.
Goals: Southern 17, Vernon 61, 87.
Ref: P Armstrong (Berkshire).