With winds gusty up to force seven, Alderney made the most of home advantage to hold the game to 0-0 at half-time.
But they have not won a match in the Muratti since 1920 when they beat Guernsey in the final to lift the trophy for the only time in its history, and the Greens were in no mood to be on the wrong side of history on this occasion.
A brace of goals from Charlton Gauvain, and efforts from Keene Domaille and Matt Loaring settled the tie before Rio Bowditch scored a consolation for the hosts, their first against Guernsey since 2007.
The final takes place at Springfield on Saturday 18 May with the Greens looking to break a four match losing streak against Jersey.
Alex Scott made his first appearance for the England U21s when he came on as a 75th minute substitute in their 5-1 win against Azerbaijan.
Rugby
Guernsey Raiders were far from their best as they came away with all the points when bottom side North Walsham visited Footes Lane.
Raiders eventually took the game 41-28.
It was a game marred by sloppy handling, the visiting backs at times dancing through the defensive line at will, and Guernsey’s forward display proving vital.
Raiders sit 11th in National 2 East with three more games to go.
Next up is the visit of Old Albanians on Saturday 6 April.
In Counties 2 Hampshire, St Jacques Vikings kept up their winning streak with a 45-12 victory at Fordingbridge.
They are third, 12 points off top of the table Sandown & Shanklin with two games in hand.
Sandown beat United Services Portsmouth 35-13 on Saturday.