As minor premiers, the Lions had lost just two games for the season and thrashed the Falcons by 56 points when they met in the second semi-final two weeks prior to the grand final.
But it was a different story in rainy conditions at Subiaco Oval with the Falcons winning the flag 5.9 (39) to 3.7 (25).
West Perth was five points down at the final change but kicked the term’s only three goals to emerge victorious.
Midfielder Aidan Lynch, who was awarded the Prendergast Medal as the competition’s best player on Monday, took a match-high 25 disposals, while landing eight tackles and a goal.
But it was 2013 league premiership player Shaun Marusic who claimed the Merv McIntosh medal as best afield with 18 disposals, five marks, six tackles, five inside-50s and a goal.