Despite losing pacemen Andrew Tye and Jason Behrendorff to international duties, WA's attack strangled Tasmania, bowling the Tigers out for 207 with one ball to spare.
David Moody took 3/47 and Jhye Richardson 2/40, as all six bowlers picked up wickets, including debutant Matt Kelly, to showcase WA's enviable depth.
Tasmanian captain George Bailey won the toss, but wickets fell at regular intervals throughout the innings, slumping to 6-99 in the 30th over, when all-rounder James Faulkner was caught down the leg side.
The visitors were in serious trouble until a 93-run seventh-wicket partnership between Jordan Silk (80 off 86 balls) and debutant Tom Rogers (38) restored some respectability, before being bowled out in the last over.
In the second innings, WA’s seasoned openers Shaun Marsh (62) and Michael Klinger (45) put on a batting masterclass with a 108 run partnership to set the pace.
Skipper Mitch Marsh (67*) and Cameron Bancroft (29*) finished off in style, Marsh hitting a whopping 7 fours and 3 sixes off just 49 deliveries. WA reaching the target in the 36th over and claiming a bonus point.
WA take on Queensland next Wednesday 11 October when the JLT One-Day Cup moves to Sydney.