Western Australia 141 and 104 for 7 (Bancroft 44*, Tremain 5-29) trail New South Wales 276 (Davies 129, Henriques 51) by 31 runs

After Davies' superbly-constructed 129 had built a lead of 135, Tremain produced a stunning opening spell of 5 for 12 in nine overs as Western Australia sank to 34 for 6 to briefly threaten their lowest even Shield total of 41.

Davies, the 23-year-old who has predominantly been a white-ball player and has reached Australia A level, was overlooked for NSW's first three Shield games this season but earned a spot at the SCG in place of the injured Jack Edwards.

On the first evening Davies had walked in with the home side tottering on 71 for 4 amid fears NSW's batting woes could rear their head again, but he responded with a 117-ball century, reaching the landmark with a six over long-on.

"They brought the field and I said to myself, if this is tossed up, I'm hitting the ball quite nicely and I back myself to get it over," Davies told ESPNcricinfo. "I've been hitting a lot of balls trying to push myself back into the Shield team and was nice to get a hundred first crack back.

"I've been overlooked at times for the red-ball side so for me I really did want to make a statement and show everyone that I can play red-ball cricket. Thought I did that today and helped put our team in a pretty good position."

When he was last-man out, NSW had built a strong lead and they quickly started to make it count on a pitch that had offered plenty of assistance with the new ball.

Tremain was already their leading wicket-taker for the season and was soon growing his tally in dramatic fashion. He started by having Sam Whiteman caught down the leg side, then pinned Teague Wyllie and Hilton Cartwright lbw with consecutive deliveries to bring tea.

On resumption, the hat-trick ball zipped past Josh Philippe's edge but he did not last long before nicking into the slips. Tremain's five-wicket haul arrived in just his seventh over when Ashton Turner shouldered arms and the ball clattered the top of off stump.

NSW had resumed on a precarious 78 for 4 but they were soon making brisk inroads towards Western Australia's total.

Davies batted at an excellent tempo and did not take undue risks, but also kept the bowlers under pressure. On 99 he showed the confidence to dance down the wicket to Rocchiccioli and launch him over long-on to bring up NSW's first century of the Shield season.

"My natural batting is quite aggressive, so I said to myself if I faced 100 balls I'd be close to 100 or 150 I'd be close to 150," Davies said. "So for me it was just batting as long as I could and I knew scoring opportunities would present themselves along the way. It worked, so pretty stoked."