Tahvon Campbell booked Forest Green a spot in the second round of the Carabao Cup for the first time in their history as they beat Swindon 1-0 at the County Ground.
Campbell slotted the away side into a 60th-minute lead after he robbed the ball from Olly Lancashire and beat Lawrence Vigouroux when one-on-one with the goalkeeper.
The goal was against the run of play as Swindon dominated the first half and had started the second brighter.
Martin Smith got the crowd up off their feet in the 14th minute when he hit the post with a speculative shot from inside his own half after a botched clearance by Forest Green goalkeeper James Montgomery landed at his feet.
Keshi Anderson tested Montgomery with a close-range header as Swindon continued to look the more likely to take the lead.
Michael Doughty warmed Montgomery's palms twice with long-range strikes, but could not break the deadlock, while the visitors were limited to half-chances such as Hayden Hollis lashing over the bar from distance.