Marcus Stoinis hit Australia's fastest T20 fifty off just 17 balls to propel the defending champion to a seven-wicket win against Sri Lanka at the Twenty20 World Cup on Tuesday.

Australia scored 158-3 in the Super 12 game in response to Sri Lanka’s 157-6 to win with 21 balls to spare.

Australia overcame a spot of bother at 89-3 in the 13th over as Stoinis came to the rescue with 59 not out — including six sixes and four fours — off just 18 balls.

He shared an undefeated 69-run stand for the fourth wicket with skipper Aaron Finch (31 not out).

Stoinis humbled the much-vaunted Sri Lankan spin attack with legspinner Wanindu Hasaranga conceding five sixes and costing 53 runs in three overs.

It was a brilliant display of power hitting by the Australians after an 89-run thrashing by New Zealand in the tournament opener. Australia will now play rival England in a crucial game on Friday at the Melbourne Cricket Ground.

Sri Lanka was asked to bat first on a lively pitch, got off to a slow start and managed just 63 runs in the first half of the innings before picking up momentum in the second to post what it hoped would be a competitive total.

The Australian trio of Josh Hazlewood (1-26), Pat Cummins (1-36) and Mitchell Starc (1-23) pegged down Sri Lanka's top order with relentless pace.

Cummins got rid of danger batter Kusal Mendis (5) in the second over when the opener skied a catch to Mitch Marsh.

A 69-run stand between opener Pathum Nissanka (40) and Dhananjaya de Silva (26) anchored the top order. Charith Asalanka (38 not out) and Chamika Karunaratne (14 not out) shared 37 runs for the seventh wicket.

The pair took 20 runs off Cummins in the last over.

Asalanka was the most enterprising of the Sri Lankan batters, hitting three fours and two sixes in his 25-ball knock. The entire innings produced two sixes and 12 boundaries as the Sri Lankan batters struggled to clear the big boundaries unlike the Australians.

Sri Lanka won its first game against Ireland by nine wickets.