Shane Watson's place in the World Cup picture has become a little less stable, after Mitchell Marsh announced himself as Australia's new No.3 with a man-of-the-match display in the thrashing of Zimbabwe.

Australia showcased their awesome batting potential ahead of next year's ODI World Cup on home soil, with allrounders Marsh and Glenn Maxwell cutting loose in a blistering partnership of 109 off 54 balls which set up a record 198-run win in Harare.

Quick Single: Maxwell magic sparks Australia

Scoring at seven an over, Australia went into overdrive when Maxwell (93 off 46) came to the crease, blasting 147 runs from the last 10 overs to post a total of 6-350 that was never threatened as Zimbabwe folded for 152.

Marsh said he was told by captain Michael Clarke before leaving for the tri-series in Harare that he had an opportunity to cement himself high up the order at No.3, a position he hasn't batted in since he was a junior.

Watson boasts a world-class record batting at the top of the order at ODI level, but at 33 and with a knack for his body letting him down, it isn't a great time for him to be sidelined by injury as Marsh grabbed his chance by clubbing 89 off 83.

Another freakish innings by @Gmaxi_32 ! @mitchmarsh235 showing his class. Great start boys. — Shane Watson (@ShaneRWatson33) August 25, 2014

With Maxwell and James Faulkner also firing, there may only be room for so many allrounders in the XI come World Cup time.

Marsh, who had been out of the side for over a year, says he's matured off the field after a chequered history of disciplinary issues and declared he's ready to meet the lofty expectations set for him by the Australian hierarchy.

"I don't think turn the corner is the right way to put it but we all know I've probably had a few ups and downs but my big focus over last 12 months has been progressing as both a person and staying on the park," said Marsh after his maiden ODI 50.

"Hopefully I can keep doing that. It's been a great few months.

"(The team) has certainly shown a lot of faith in me and hopefully I can repay that. I feel like I'm ready to take on that challenge.

"If you score enough runs and take enough wickets you're going to be playing for Australia."

Marsh spent some of his childhood in Zimbabwe when his father Geoff served as the national coach, and he's also revisited in recent years for Australia A.

The Australians now turn their attention to South Africa on Wednesday and Marsh says he holds no fear against the likes of Dale Steyn and Morne Morkel.

"I'm certainly not scared," he said.

"It's almost my second home now I've played (almost) more cricket here than at the WACA."