Western Australia, aided by centuries from Justin Langer and Adam Voges, amassed an impressive 607 for eight in reply to News South Wales' first innings of 305 and grabbed a swag of wickets before stumps to take the initiative on Saturday.
New South Wales was 184 for four at the close of play -- still trailing by 118 runs.
Western Australia needs an outright win to reclaim the top spot from Queensland after they defeated South Australia.
South Australia had capitulated, losing their last nine wickets for 34 as Queensland wrapped up a win in Brisbane.
Only Darren Lehmann (104 from 85 balls) and Greg Blewett (54) offered any resistance as Man of the Match Joe Dawes claimed five wickets for match figures of 8-88.
Lehmann and Blewett looked set to guide South Australia to victory before Lehmann had his middle stump sent flying by Mitchell Johnson to leave them at 166 for two.
Lehmann's dismissal sparked a collapse with nine wickets falling in less than 15 overs.
A quickfire stand of 120 between Jason Arnberger and Brad Hodge against Tasmania kept alive Victoria's season in the match at the Melbourne Cricket Ground.
Arnberger raced to 67 not out and Hodge followed his first-innings 140 with 52 not out to spirit Victoria to 121 for one at stumps on day three - a lead of 252 runs with a day to play.
Michael Bevan scored 144 in Tasmania's first innings of 346 - the left-hander's sixth century this season.
Test leg-spinner Shane Warne picked up the last three wickets to finish with 3-99.
Brisbane (day three): Queensland 199 (C Perren 58, A Bichel 47 not out, L Steves 46; S Tait 4-61, P Rofe 3-44) and 257 for 8 (C Philipson 64 not out, M Love 35; D Cullen 5-78) beats South Australia 143 (G Blewett 41, R Harris 32; A Noffke 3-22, J Dawes 3-39) and 200 (D Lehmann 104, G Blewett 54; J Dawes 5-49, M Johnson 3-23).
Melbourne (day three): Victoria 477 for 8 declared (B Hodge 140 not out, M Elliott 89, C White 75, J. Arnberger 60; A. Griffith 6-124) and 121 for 1 (J Arnberge 67 not out, B Hodge 52 not out) Vs Tasmania 346 (M Bevan 144, T Birt 57; S Warne 3-99, J Moss 2-21).
Perth (day three): New South Wales 305 (D Thornley 100, P Jaques 50; B Williams 4-53, A Voges 2-43) and 184 for four (P Jaques 73, G Mail 63; M North 3-62, B Edmondson 1-47) Vs Western Australia 607 for eight-dec (J Langer 134, A Voges 128; S Clarke 4-167, N Bracken 2-89)