Evergreen batsman Matthew Phelps and fickle weather have stalled Western Australia's victory charge and fuelled hopes of a NSW escape in the Pura Cup cricket match at the Sydney Cricket Ground.

Following on 391 runs behind after being skittled for 117 in its first innings, NSW was 3-235 in its second dig when play on day three was abandoned in the final session because of bad light and a storm.

Coming in at number three following the dismissal of Phil Jaques (2), Phelps (124) added 86 for the second wicket with former Warrior Craig Simmons, whose 43 was his highest first class score.

The 33-year-old right hander then added 143 off 182 balls in two hours with Dominic Thornely (56 not out), before being dismissed just three minutes before play stopped.

The forecast for Friday, when 112 overs are scheduled, included the possibility of an afternoon shower or thunderstorm.

While NSW still required another 156 to make WA bat again, Phelps felt the Warriors' history at the SCG, where it has only won outright seven times in 47 games, offered the Blues some hope of an unlikely win.

"If we were to score quite quickly in the morning, the history of the West Australians playing at the SCG batting last isn't that great from their perspective, certainly that's something we know about," Phelps said.

"Probably the best time to bat is with the new ball. Once the ball gets a little bit old, it loses its shine and we can get the ball to go Irish. Plus we've got (off spinner) Jason Krejza who bowled well, and Stuart MacGill a Test leg spinner.

"Funnier things have happened, so you never know."

Phelps struck 19 boundaries in his impressive 178-ball, 215 minute innings, which produced the sixth first class century of his career.

On course for his most prolific season, Phelps has this summer doubled his tally of first class hundreds from the six previous seasons, adding Thursday's ton to two scores of 133 against Tasmania at the SCG and Victoria in Lismore.

Phelps said he was more relaxed this season after playing a full summer last season following years of being in and out of the team.

"I've worked on a few extra shots, and it's probably given me more scoring options around the ground and so its created greater pressure on the bowlers, I'm just trying to stay one step ahead," Phelps said.

Paceman Steve Magoffin (2-26 off 11 overs) was WA's only multiple wicket taker in the second innings, during which Beau Casson (0-77 of 14) came in for some fierce treatment from Phelps and Thornely, who reached his 50 with an off driven six off the promising wrist spinner.

NSW added 40 runs for its last three first innings wickets after resuming at 7-77, but the entire innings lasted just 39.5 overs.

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