The Falcons fielded a strong team for the clash, with a number of players returning from duties in the league side, which did not qualify for the finals.
But the Lions kicked five straight goals to 1.1 in the first quarter and never looked back in a 15.8 (98) to 5.12 (42) victory at Leederville Oval.
The Falcons could not produce any multiple goal-scorers.
Cameron Branch, Corey Chalmers, Ben O’Regan, Drew Rohde and Mitch McPhee booted one goal each.
In contrast, Subiaco produced three multiple scorers. Kyle Halligan led the way with six majors.
West Perth kept the Lions at bay in the third quarter.
Subiaco responded in a similar fashion to how it began the match, kicking five goals to one in the last quarter to run out with a near 10-goal triumph.
West Perth returns to Leederville Oval to face Claremont in the preliminary final on Sunday.