Jess Stevenson reports.
Despite going in 12-0 up at half-time, Guernsey were outplayed by a resurgent Barnes at Foote's Lane.
National League Three London and South East high-flyers Barnes scored 19 second-half points without reply.
GRFC scored their first try and conversion eight minutes into the game, but failed to convert a second try 20 minutes later.
Their lead of 12 - 0 at half time was quickly kicked into touch when Barnes came out fighting for the second half.
Within the first five minutes Barnes had scored their first try and conversion, followed by another 10 minutes later. A third not long after saw them take a clear lead and a final score of 19.
GRFC player coach Jordan Reynolds said the team had a game plan they had not managed to stick to in the second half.
"Rugby is a game of momentum. In the first half we had that, in the second half we missed the line out and then we missed a tackle, which wasn't happening in the first half, and then they scored straight from that.
"Any mistake you get punished for and I think today we just got punished for our mistakes."
He said the result had been there for the taking.
"You could see how happy they were to get the win. We just have to keep our form up for 80 minutes."
But overall Reynolds said Barnes were a good side and Guernsey had held its own.
With thanks to Dave Doonan.