Guernsey thrashed Alderney 4-0 to seal their place in the final of the Murrati Vase against Jersey.
Goals from Tom De La Mare, Tom Martin, Craig Young and captain Angus MacKay made sure of Guernsey's progress
Guernsey fielded a youthful side, with the island's main club side Guernsey FC - who play in Ryman League South - also in action on Saturday.
"We played well and did the job. We didn't make any assumptions we were going to win," McKay told BBC Guernsey.
"Alderney put up a really good fight and made it difficult for us.
"It was a good game but the main thing was to make sure we got into the final against Jersey, because we wouldn't forgive ourselves otherwise."
Guernsey coach Steve Sharman said the team's display - with several regular members of the squad unavailable as they were involved in Guernsey FC's 1-0 defeat by Merstham - showed that the island was developing good strength in depth.
"They did extremely well. We enjoyed ourselves and it was a good experience for our players," he said.
"It shows we've got a great amount of talent and we were able to put out two strong groups."
Alderney have not made the final of the annual Channel Islands tournament since 1938.
Manager Alan Adamson said his players had shown good character despite the one-sided scoreline.
"I wasn't too pleased with the first half," he said.
"We didn't stick to the game plan, but in the second half we got it sorted out and I think we did ourselves proud."