Australia skipper Aaron Finch termed his knock "unusual" and "poor" after struggling to 31 off 42 balls in his side's seven-wicket win over Sri Lanka in the T20 World Cup here on Tuesday.

Even as Finch was unable to break the shackles, Marcus Stoinis recorded the fastest fifty by an Australian to help his side overhaul a target of 158 in 16.3 overs. Stoinis raced to an unbeaten 18-ball 59, having reached his half century in 17 deliveries.

But Finch, who usually looks to attack, seemed to be batting on a different pitch.

"Very happy (with the result). My innings was unusual, poor. I couldn't hit the ball," Finch said at the presentation ceremony.

Defending champions Australia entered the game after their humbling defeat to New Zealand in their opener.

"The way we approached with the bat was fine. It was seaming a long way there, if we could get through that, it was important to set-up the back end of the innings.

"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."

Charith Asalanka's 38 not out off 25 balls helped Sri Lanka put up a fighting 157 for six after Australia put them in.

Sri Lanka fought hard before they were blown away by the brute force of Stoinis.

Asked about the powerplay, Finch said, "They bowled the hard length, it was tough. Such a big ground, hard to stand and deliver. Nice to get the two points."

Speaking about Stoinis' knock, the Australian captain said, "It was a pretty special innings. To come out with that intent is the main thing. When you walk out to bat and have that presence of the crease, that's half the battle in T20 cricket.

"When you got the skill that he has got, it's a good combo."

Playing in front of his home crowd, Stoinis said he was nervous to start with.

"To be honest I was really nervous today being at home in Perth with lots of family and friends here but really happy we put on a bit of a clinic today.

"Mentally I was nice and fresh having some time off with this side strain, but so far so good. I felt good," Stoinis said.

Sri Lanka captain Dasun Shanaka felt his pacers are not 100 percent in terms of fitness.

"I think the fast bowlers especially are not prepared well. They are coming after injury so I think that's the reason behind them getting injured most of the time.

"It was really tough with the new ball. It's too hard to get going. Even Finch struggled with the new ball. It was the latter part that they played really well," Shanaka said.