Luke Norris' first-half penalty sent 10-man Gillingham into round two of the Johnstone's Paint Trophy as they beat Stevenage 1-0 at the Lamex Stadium.
Norris converted from the spot in the 17th minute after Gills striker Cody McDonald was clumsily fouled by Boro goalkeeper Chris Day.
Day, who was lucky to escape punishment for an earlier tangle with Norris, was only booked.
Despite sitting 26 places apart in the league pyramid, the hosts created chances throughout. Former Gillingham midfielder Charlie Lee shot narrowly wide with a low effort on the turn after 24 minutes and flicked Jerome Okimo's cross past the post shortly before the break.
Summer signing Connor Calcutt almost bundled in following a goalmouth scramble on the stroke of half-time and forced Gills goalkeeper Glenn Morris into a fine save from point-blank range.
Norris came the closest to adding a second for the visitors, who had defender Gavin Hoyte sent off for a two-footed lunge on Roarie Deacon after 63 minutes, but his low shot was well saved by Day.