New South Wales 7 for 165 (J Sangha 66*, Kelly 3-22) trail Western Australia 6 for 356 dec (Bancroft 117, Cartwright 81, S Marsh 58) by 191 runs

Some inspired seam bowling from Western Australia's Matthew Kelly and Joel Paris produced a stunning New South Wales batting collapse at Bankstown Oval to turn a near-certain draw into a possible Sheffield Shield win for the visitors.

With both teams vying for a spot in the final, the middle-session on day three of this rain-affected penultimate-round fixture may prove to be pivotal in the course of the season.

Kelly picked up wickets in three successive overs leaving the home side limping their way to tea at 5 for 55, as a hitherto benign pitch seemingly turned into a minefield.

Kelly's swing firstly undid Blues' skipper Kurtis Patterson without playing a shot before Jack Edwards and Hayden Kerr were also sent packing.

At the other end Paris started the rot by picking up the crucial wicket of opener Daniel Hughes caught at second slip.

Jason Sangha's lone knock kept the innings together with the 22-year-old digging in to end the day unbeaten on 66.

An injured Moises Henriques, who came in at No. 8, led a brief revival only to tickle a catch down the leg side off the bowling of rookie spinner Corey Rocchiccioli on 23.

Chris Tremain swiped three sixes late in the day to reach 41 not out, and lift the home side closer to the follow-on mark of 207 in an unbroken stand of 67 with Sangha

The two sides are among five states with five wins apiece vying for a spot in the March 31 season decider.

After the entire day two was lost due to rain, Western Australia resumed at 3 for 231 and continued on comfortably enough before closing their innings half an hour after lunch.

Hilton Cartwright looked set for a ton but his watchful 209-ball innings ended on 81 when he was caught hooking a Tremain delivery while seeking to up the scoring rate.

Tremain's second wicket came a day and a half after his first with day two lost due to ongoing showers. Cameron Bancroft had top-scored for WA with 117, before he was dismissed by Tremain late on Tuesday.

The hard-hitting D'Arcy Short was the only Western Australia batter who failed to reach double figures when he was caught and bowled by Kerr for 1.

Aaron Hardie remained unbeaten on 37, while allrounder Edwards was the pick of the Blues' attack returning 3 for 58 off 21 overs.