The talented Piastri, who grew up a few miles down the coast from Albert Park, was thrilled to finish eighth as eight rival cars fell by the wayside.
"Chaos is how I would sum that up. Crazy race. I think that’s the first race I’ve been involved in with three red flags," Piastri told reporters.
"Happy to be in the points at the end of it. The pace in clean air was pretty solid, just got stuck behind Yuki for a while. But happy to get my first F1 points."
With Lando Norris (23) coming sixth, it was a good day for McLaren, who came to Australia without any championship points.
They now have 12 to lie fifth in the constructors' championship behind Red Bull (123), Aston Martin (65), Mercedes (56) and Ferrari (26).
Norris, who passed Haas's Nico Hulkenberg (35) and AlphaTauri's Yuki Tsunoda (22), said it was the first positive day for McLaren in terms of pace but he blamed the tyres for contributing to the slew of crashes.
"You would think a heated tyre to 60 or 70 degrees would give us some grip and it doesn’t," he said.
"Like at the end, this final lap, I felt like I’m going to crash on every single corner it’s that bad."
McLaren boss Zak Brown said the team were happy with the points but clearly had a straight-line speed deficit to rivals and expected upgrades might not benefit them noticeably at the next race in Baku in three weeks.
He added that Piastri already looked like he could give Norris a run for his money.
"I think Oscar just needs a little bit more experience to put it together on a lap-by-lap basis in the way Lando can," Brown said.
"But I think we’ve got two good racing drivers, that’s for sure."
