In the first encounter since the introduction of eligibility rules for the professional Championship outfit in the annual clash, the Reds emerged 33-19, but only after coming from 19-13 down shortly after half-time.
Guernsey scored tries through Cameron Craine, Ned Brown and Sam Whitehead, but were badly hit by the loss of fly half Owen Thomas just before half-time to a suspected fractured ankle.
Earlier in the day, the Guernsey Ladies had retained their Siam trophy with a convincing 41-12 win, running in seven tries in the process.
Guernsey also won the Nash Cup for veterans while Jersey won the second-team Fallaize Cup.
Full reports in Monday's Guernsey Press.
