Aaron Finch was left with mixed emotions after Australia beat Sri Lanka in the Cricket World Cup but he "couldn't hit the ball" in a "poor" innings.

Australia started the defence of their title by suffering an 89-run defeat to New Zealand in a repeat of last year's final, but the hosts responded with a seven-wicket victory at Perth Stadium on Tuesday.

Marcus Stoinis was the star of the show, blasting a record-breaking unbeaten 59 from only 18 balls to get the holders home with 21 balls to spare and move them into fourth place in Group 1.

The powerful all-rounder cleared the rope six times and struck another four boundaries to register Australia's fastest T20I half-century and the joint-second quickest in a T20 World Cup, passing 50 from only 17 deliveries.

Finch finished on 31 not out from 42 balls after watching Stoinis cut loose at the other end, and the captain gave a frank assessment of his scratchy knock.

He said in the post-match presentation: "I'm very happy [with the win]. Obviously my innings was unusual. It was poor. I just couldn't hit the ball. But I thought the way that we approached it with the bat was fine.

"It would've been nice if I could've kicked on earlier and made the chase a bit easier but all in all, pretty clinical, I think with the ball as well.

"They bowled a hard length. It was tough. It's such a big ground that you feel as though it's hard to just stand and deliver. Especially with a bit of extra bounce and when the ball is seaming slightly, you feel it's just not quite as easy to hit the middle of the bat. That's no excuse for the way I played, but it's nice to get two points."

A sensational fifty from Marcus Stoinis powers Australia to a spectacular win #AUSvSL | #T20WorldCup | : https://t.co/pRsIxO6aDz pic.twitter.com/urcZqczGAW
— T20 World Cup (@T20WorldCup) October 25, 2022

The opener praised Stoinis following his sensational exhibition of clean striking.

"It was a pretty special innings," skipper Finch said. "To come out with that intent is the main thing. When you walk out to bat and you have that presence at the crease, that's half the battle in T20 cricket. When you have the skill and the strength that he's got, that's a pretty good combo."

Australia's next assignment will a mouthwatering clash with England at the MCG on Friday.