Simple skill errors and a lack of forward firepower cost the reigning premiers in a 9.11 (65) to 7.6 (48) loss to the Sharks at Arena Joondalup.
The victory left West Perth four games out of the top four with only three rounds remaining, and the side will end the season in the bottom five.
The Falcons have slipped to sixth place after a Claremont win over Perth moved the Tigers into fifth.
The East Fremantle triumph extended the side’s winning streak at Arena Joondalup to six games, the Sharks having not lost at the ground since 2009.
The visitors led at every change in a high-pressure contest that forced errors from both sides early before East Fremantle took control.
The home team was a chance to steal the match heading into the last quarter, at just 13 points down.
But the Sharks were dominant in the final stanza, albeit without much success on the scoreboard, with the ball spending little time in West Perth’s forward half.
Dangerous attacker Brett Peake finished with five goals for East Fremantle.
On-baller Aaron Black took 30 disposals to lead the Falcons’ possession count.
West Perth’s Steve Potente was solid on return from injury, applying much-needed forward pressure in a 20-possession, five-tackle performance.