A century from Caleb Jewell lifted Tasmania's innings in the One-Day Cup match in Hobart and set undefeated Western Australia a challenging victory target.
In an innings trimmed short by rain delays, Tasmania reached 6-285 off 48.4 overs after winning the toss batting at Bellerive Oval.
Opener Jewell was out for 104 from 117 balls, having posted his third 50-over century in his 28th match.
The other major contributors were Jordan Silk and Mac Wright who shared a quickfire 80-run stand for the fourth wicket.
Captain Silk made 62 from 65 balls, while Wright was run out for 44 made off just 32 balls.
Opening bowler Jason Behrendorff (2-42) dismissed dangerman Ben McDermott (13) early on, and returned to snare Jewell caught behind.
Spinner Ashton Agar was a notable inclusion for WA following his early return from the Test tour of India, with the left-armer picking up the wicket of Jake Doran (36) and returning tidy figures of 1-38 from his 10 overs.
Regardless of the result, Western Australia are assured of top spot and will host the final on March 8.