Western Australia 2 for 18 trail New South Wales 180 (Patterson 72*, Morris 5-36) by 162 runs

Patterson was left stranded on 72 off 149 balls, with the left-hander a class above as wickets tumbled around him.

In reply, WA stumbled to 2 for 18 at stumps, with openers Sam Whiteman and Cameron Bancroft falling to Dwarshuis on his Shield debut, the left-arm quick striking with his first delivery in first-class cricket when Whiteman edged to slip. Debutant Sam Fanning and Hilton Cartwright ground their way to stumps.

Morris was the hero of the day, with the 24-year-old's second five-wicket haul putting WA in the box seat before the late stumble.

"I'm just starting to understand my role within the team," Morris said. "I've got a licence to bowl fast and intimidate. I'm settling into my role nicely now, and I'm enjoying it.

"We'll regroup tomorrow. We know NSW are going to come pretty hard early tomorrow, but hopefully we can blunt that and pile on a few runs."

NSW crawled to 0 for 30 off 18 overs before Morris inflicted an important double blow. Daniel Hughes was the first to fall when he struck Morris straight to mid-off, and they were 2 for 37 when a diving Paris took a sharp catch at gully to dismiss Blake Nikitaras.

Morris, who was clocked around 145kph, found the edge of Jason Sangha after lunch, and he had his fourth wicket when he bowled Baxter Holt. The five-wicket haul was complete when Morris dismissed tailender Chris Tremain. Paris and spinner Corey Rocchiccioli helped clean up the middle order and tail.

Patterson's patience proved crucial in helping NSW avoid a complete crumble like they experienced in their nine-wicket one-day loss to WA on Saturday.

In that match, NSW slumped to 6 for 20 before being rolled for 76, with WA needing just 17 overs to reach the victory target.

Patterson's half-century has at least given NSW something to work with in the Shield match, but WA remain in the box seat to take a sizeable first-innings lead.

They kicked off their title defence without star duo Shaun Marsh (knee) and Jhye Richardson (rested).