The 23-year-old was challenging McLaren teammate Lando Norris for the lead when the two papaya cars slipped off the road on lap 44 of 58.
Both came unstuck at Turn 12 amid the arrival of a rain shower, but while Norris recovered quickly and scurried to the pits for intermediates, Piastri was not so fortunate.
To the horror of the patriotic Australian crowd, Piastri spun on the wet grass and became stranded, eventually reversing into the escape road and rejoining almost a lap down.
“I tried to push a bit too much, I guess,” recounted Piastri, who dropped to 13th before recovering to finish ninth.
“In those conditions, it’s very difficult to judge just how slippery it’s going to be. I think from one lap to the next, it had really changed a lot.
“You know, I could see Lando going off in front of me, but I was also already in the corner, basically, so there wasn’t much I could do to slow myself down at that point.
“Then once you’re in the gravel, in the grass, you obviously try to keep the car as straight as possible.
“And then obviously to get stuck in the grass like that was pretty unbelievable, sat in the car, but I’ve only got myself to blame for being there.”
Speaking a short time after the race, Piastri was able to find some levity amid the disappointment of the situation.
“Good thing I spent some time in the off-season trying to learn how to reverse a tractor on Jeremy Clarkson’s farm,” he said. “I think it came in handy today.”
Piastri had qualified second to Norris but fell to third behind Red Bull’s Max Verstappen as he struggled for grip on the wet track at the exit of Turn 1.
A mistake from Verstappen eventually let Piastri back to second and enabled the Aussie to show his true speed.
After an initial call to hold position, Piastri was told he was free to race his teammate but could not find a way by before the fateful moment.
While Piastri was unable to become the first home hero to finish on the podium in an Australian F1 Grand Prix, he takes plenty of positives out of the weekend.
“I think for essentially 56 laps of today’s race, I was very proud of the job I did,” he said.
“I felt like the pace was really strong and, I’m obviously disappointed with the mistake I made, but that doesn’t take away completely from how strong the whole weekend has been.
“Not just the team, but for myself, like I’ve done a good job all weekend. So I think it would be pessimistic of me to just write off the whole weekend because of one mistake.”
