Alan Navarro scored twice on his debut to send Swindon through to the second round of the League Cup at the expense of his former club Brighton.
The visitors looked in control in the first half but were left stunned by a revitalised Swindon after the break.
Paul Benson gave Town the lead from Navarro's well-worked free-kick.
The ex-Seagulls midfielder opened his account when he hooked the ball into the top corner, and made it 3-0 with a deflected shot over Tomasz Kuszczak.
VIEWS FROM THE DRESSING ROOM
Swindon Town midfielder Alan Navarro told BBC Wiltshire:
"I couldn't ask for any more. It was a great performance from the boys.
"I'm not used to getting two goals in a game. It topped off a great night against my old team.
"It wasn't just about my goals; the whole team performed to a point where Brighton couldn't break us down.
"The gaffer told us to just keep believing we could win the game and that's what we did."
Swindon Town 01 Foderingham 02 Archibald-Henville 03 McEveley 05 Devera 06 Navarro Booked (Ferry - 82' ) 10 Ritchie 12 McCormack 18 Miller 14 Benson (Storey - 89' ) 16 Williams 23 De Vita (Rooney - 87' ) Substitutes 30 Bedwell 04 Flint 15 Thompson 07 Rooney 08 Ferry 13 Risser 20 Storey Brighton & Hove Albion 29 Kuszczak 02 Bruno 03 Greer 05 Dunk 28 Bridge 11 Noone 15 Vicente 17 Harley (Calderon - 56' ) 18 Dicker (Agdestein - 66' ) 26 Bridcutt 09 Barnes Booked Substitutes 16 Ankergren 06 El-Abd 14 Calderon 22 Painter 38 Dickenson 36 Oatway 23 Agdestein