Marcus Stoinis has pummelled Sri Lanka's attack with the fastest 50 in Australian Twenty20 international history (53 off 17 deliveries) to lead Australia to a seven-wicket victory in the T20 World Cup in Perth.

Stoinis finished his innings with six sixes and four fours to be 59 not out along with captain Aaron Finch (31no), who carried his bat through what was an unconvincing innings.

Stoinis's innings was the equal second fastest 50 in T20 World Cup history — tied with Dutchman Stephan Myburgh, who achieved it in 2014 against Ireland — and behind India's Yuvraj Singh, who scored one off just 12 balls against England in 2007.

The match initially turned in Australia's favour when Stoinis's fellow all-rounder Glenn Maxwell came to the crease with Australia at 2-60, having just lost Mitchell Marsh and with a struggling Finch at the other end.

Maxwell set Perth Stadium alight as he launched the ball to and over the boundary with ease, before Sri Lankan quick Lahiru Kumara launched a bumper barrage at Maxwell.

It troubled the Australian, who was hit on the gloves with one bouncer before being hit in the throat with a nasty one that reared as he played a pull shot.

Maxwell was a shell of his former self after that and added one more run before he was spectacularly caught on the boundary in the next over by Ashen Bandara off the bowling of Chamika Karunaratne.

The exit of Maxwell might have brought Sri Lanka some relief and hope with Australia suddenly 3-89, but Stoinis extinguished that.

The West Australian was all business and took the Sri Lankan attack apart with some lusty blows as he hit Australia to victory in quick time.

His 59 not out came off just 18 deliveries, where he took 18 off Wanindu Hasaranga's 15th over himself before he hit three sixes in the next off Maheesh Theekshana to make it to 50 off 17 balls, eclipsing the mark Cameron Green set just last month ago against India.

The winning runs came from Finch in the next over as Australia improved to 1-1 in their title defence, after losing their tournament opener to New Zealand.

Finch was full pf praise for Stoinis and ridicule for himself post match.

"To come out with that intent is the main thing.

"When you walk out to bat and have that presence, it is half the battle in T20 cricket and when you have the strength and the skill that he's got it's a pretty good combo.

"I'm very happy ... obviously my innings was poor, I just couldn't hit the ball but I thought the way we approached it with the bat was fine."

The innings from Stoinis turned the tide of the match as up until his arrival at the crease the game had been tight.

At various points Sri Lanka, who had to play through the tournament preliminaries to make the final group stage, looked to be on top and it was the case early during their innings.

Despite losing opener Kusal Mendis in the second over to Pat Cummins, they looked to be cruising towards a good total with Pathum Nissanka and Dhananjaya de Silva building the innings.

But de Silva fell to an excellent diving catch from David Warner off the bowling of Ashton Agar before Nissanka was run out at the hands of Marsh and Mathew Wade for 40, triggering a collapse as they went from 3-97 in the 14th over to a total of 6-157, which Australia would duly chase down.

Australia will next play England on Friday October 28 at the MCG.