The majority of the fifth-placed Falcons’ losses this season have come within two goals, but the second-placed Swans dealt the home side its biggest defeat of 2014 with a 16.9 (105) to 11.10 (76) victory at Arena Joondalup.
Former West Coast player Ryan Davis kicked five goals for the visitors, while West Perth’s Matt Johnson made his strongest league contribution of the year with 23 possessions, five marks and two goals.
East Fremantle, which has West Perth hunting its top four spot, strengthened its hold on fourth position with a 10-point win over Perth giving it a three-game buffer.
It doesn’t get any easier for the reigning premiers, who face third-placed Subiaco this weekend, before taking on league leaders East Perth with just a four-day turnaround from their Foxtel Cup grand final clash against Williamstown in Geelong.
The club’s appeal to have the derby fixture moved to Sunday was rejected by the WAFC on Friday.
West Perth, which sits on 24 points, must win at least four of its remaining seven games to give itself any chance of a finals berth.
Even then, the side would be reliant on a form slump from the Sharks or Lions, who sit on equal points with East Fremantle, to sneak past them.
The Falcons were in a similar position heading into round 16 when they missed the finals in 2012.
That season, West Perth was on 26 points in fifth spot after 15 rounds, but only two games outside the final four.
The side was unable to ascend any further, however, with just three wins from its last seven matches.