Airdrieonians got the better of Raith Rovers to set up an SPFL Trust final with either Falkirk or The New Saints.
Nikolay Todorov lashed in the only goal at Stark's Park after six minutes when Charlie Telfer picked out the unmarked striker with a neat pass.
Rovers' Kevin Dabrowski was the busier goalkeeper as Ian Murray's side slumped to a fifth successive loss.
This was Airdrieonians' third 1-0 victory over their high-flying Championship rivals this season.
The other meeting was a 1-1 draw, with Todorov on target in three of the four games.
Airdrieonians, who had player-manager Rhys McCabe filling in at centre-half, are now unbeaten in seven matches, winning five of those, as they prepare to meet Hearts in the Scottish Cup next week.
Airdrieonians player-manager Rhys McCabe told BBC Alba: "Sometimes it's about playing to the (windy) conditions and I thought we managed the game really well.
"The front two really ran their socks off and gave the platform to go and play.
"We had three or four good moments in the first half when we got in behind their midfield when we really should have done a lot better."