Piastri won seven races last season and led the drivers' championship for an extended period before surrendering the lead to teammate Lando Norris and finishing third.
The Australian also started last year on the front row at Albert Park before weather wreaked havoc with his race and left him having to recover in ninth.
While the 24-year-old concedes McLaren weren't the hot favourites they were last year, Piastri was still upbeat about the chances of becoming the first local driver to climb the podium on Sunday.
The best result for an Australian at the Melbourne event has been fourth - Mark Webber finished fourth and was equalled by Daniel Ricciardo in 2016 and 2018, and Piastri in 2024.
"The honest answer is I have no idea," said Piastri, when asked if he could win.
"I think based off testing, we seem like we're in the mix at the front.
"I certainly wouldn't be saying that we're the favourite to be winning and I don't think the picture looks quite as positive for us at the moment as it did 12 months ago.
"But I think the big caveat to that for everyone is there's so much potential still unexplored ... if you had have turned up here with the car we had the first day of testing, we'd probably be in the midfield or probably at the back."
Appearing primed for the world title, Piastri finished third in the standings behind Norris and Red Bull's Max Verstappen and admitted it took time to recover from the late-season fade.
He said the significant changes, with this year's cars having to adhere to new power unit and aerodynamic regulations, had been a blessing.
"The pre-season has been good, it's been nice in some ways to have such a new project to focus on, or new regulation to focus on," Piastri said.
"There's been plenty to get stuck into and there still is plenty still more to learn."
Arriving in Melbourne a few days ago and mobbed in the CBD, Piastri said he had been feeling the love from home fans rather than pressure to deliver a result.
"I'm not at the race weekend yet, but the support I had in the off-season, the support I had even yesterday doing a few bits and pieces around the city, it's gone up a level from last year which is really special to see," he said.
"So I think for me it's just pride really and feeling of support.
"Obviously last year's race didn't end how I wanted, but there's no extra pressure to try and make up for that or anything."
14°C