WA were looking wobbly at 4-94 after winning the toss and electing to bat, but important knocks from Green (95no) and Marcus Stoinis (79) ensured the home side ended day one well placed at 5-296.

Green started his career primarily as a bowler, but has morphed into a talented all-rounder.

The 20-year-old can't bowl at the moment while his back is managed, but his recent form with the bat has been superb.

Green scored 87no and 121no in a Shield game against Queensland earlier this month, and he posted a match-winning knock of 86 in the one-day cup to help WA reach the final.

The right-hander cracked 16 boundaries on Friday, with his unbeaten knock putting WA in a strong position.

Stoinis is backing Green to notch a century when play resumes on Saturday.

"It's only five runs. I don't want to jinx him, but he should be right," he said.

"He's going to be a superstar. Once he's back bowling, it will be pretty exciting."

Stoinis was also on track for a century until he was run out by a brilliant piece of fielding from Wes Agar.

Bancroft (12) debutant Jake Carder (13) Shaun Marsh (41) and Ashton Turner (4) were the other wickets to fall for the home side on the opening day.

Day two will get underway at the WACA Ground from 10:30am AWST this morning.