Australia's Josh Giddey warned his teammates they cannot afford another slow start at the Basketball World Cup after overcoming early struggles to beat Finland in their tournament opener on Friday.

The Boomers trailed at the end of the first quarter but came alive before half-time, eventually running out comfortable 98-72 winners on the southern Japanese island of Okinawa.

Rising Oklahoma City Thunder star Giddey flirted with a triple-double, claiming 14 points, nine rebounds and eight assists.

But the 20-year-old said his team must improve when they play Germany in their second game on Sunday.

"It's hard in FIBA because it's a shorter game -- slow starts can cost you a ballgame," said Giddey.

"We were lucky tonight, we were switched on from the second quarter onwards.

"We play Germany in a few nights and a slow start against a team like that, it's hard to dig yourself out of a hole in a short game like FIBA ball is."

Patty Mills led Australia in scoring on 25 points, followed by Giddey on 14 and Joe Ingles on 13.

The Boomers scored eight unanswered points to end the first half 45-40 ahead and did not relinquish their lead for the rest of the game.

Coach Brian Goorjian said his players "stayed with it" after a nervy start.

"We talked about, leading in, the importance of the defence -- I thought we were tremendous defensively," he said.

"It started at the end of the second quarter and right through the second half."

Finland got 19 points from star player Lauri Markkanen of the Utah Jazz.

But he was overshadowed by Giddey, who is appearing at his first tournament for Australia.

"A lot of excitement, a lot of emotions going through me when you've got your country on your back and you're trying to win for your country," he said.

"There are guys on this team who have been here for 10-15 years, so it's important to come into the team with the same mind-set and have everyone on the same page."

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