An equaliser in the injury time from Martin Williams dashed Guernsey FC's hopes of a win in their first away game in the Combined Counties League.
The island side went a goal down after Dean Peltohak gave the home side the lead on 37 minutes.
16-year-old keeper James Hamon made some crucial saves in the first period to keep Guernsey in the game.
Ross Allen came off the bench to score two second half goals, including a penalty, before Williams struck.
"The first half we struggled a bit to settle into it, we didn't earn the right to play," Guernsey FC director Mark le Tissier told BBC Guernsey.
"They had a free kick 20-25 yards outside the area and the Hartley guy struck a superb shot in the the bottom left hand corner," he commented on Williams' late equaliser.
And Le Tissier was full of praise for his young goalkeeper James Hamon, who was making his debut for the club: "He played absolutely superbly, he really showed his class and you can see that in the future he's going to be a great asset to us."