The Falcons held an eight-point lead at three-quarter time before kicking four final-term goals to two in a 12.13 (85) to 9.8 (62) victory at Fremantle Oval.
Aaron Black (33 disposals) and Trent Manzone (29 disposals) led the possession count for the second week running, with Matt Fowler booting six goals in his best performance for West Perth since arriving in 2013.
The side is a win and more than 13 percentage points clear of third-placed Peel.
For the Thunder to steal second spot, they would need West Perth to lose to Claremont by at least 100 points at Arena Joondalup on Saturday, while winning against South Fremantle by at least about 100 points themselves.
In other words, it is safe to say the Falcons � win or lose this weekend � will be hosting the qualifying final against Peel or East Perth in just under two weeks time.
Joondalup has not seen September WAFL action since 2011 when West Perth lost to Subiaco by 15 points in a blustery and wet preliminary final.
It remains uncertain what jumper design the Falcons will wear for televised finals, with the WA Football Commission still trying to resolve the clash between TV broadcaster Channel 7 and West Perth�s Channel 9 guernsey sponsorship.