Scott Davidson's late penalty gave Guernsey an important 18-15 win at Hertford in National Three London.
The centre, who was playing in just his second game for the island side, kicked the winning points as Guernsey held on after a second-half fightback.
The visitors led 15-5 at half-time as a try for Sam Stevens and a penalty try were sandwiched by Luke Sloan's score.
Hertford levelled the scores through a Robert Walters penalty and Chris Joannou try before Davidson's winner.
The win sees Guernsey rise up to sixth place in National Three London.