Melbourne - San Antonio Spurs' Patty Mills sank a game-high 30 points as Australia beat the United States for the first time ever Saturday, stunning the basketball world champions 98-94 in a huge upset.

Andrew Bogut added 16 points with nine rebounds and four assists while Joe Ingles scored 15 and seven assists in front of 52,079 fans in Melbourne -- the biggest crowd ever to watch a game of hoops in Australia.

Boston's Kemba Walker led USA with 22 points off the bench, but it wasn't enough to prevent a rare defeat for Gregg Popovich's team in a massive wake-up call ahead of the World Cup in China, which tips off on August 31.

"The support has been amazing. We're very proud to represent these fans and in the right way. We're doing it as a team, as a group," said the experienced Mills, who was electric in the fourth quarter.

"This is a building block for us, we are just taking it step-by-step. It's just nice to see our progress."

Popovich's squad lacks a host of top NBA stars with the likes of LeBron James, James Harden, Anthony Davis and Kawhi Leonard all opting out of the World Cup.

But it still boasts a host of young talent and they comfortably won against Australia 102-86 in a pre-World Cup warm-up on Thursday, on the back of a 90-81 victory over second-ranked Spain in California this month.

But they couldn't cope with the Boomers' offence, giving up a 10-point third-quarter lead to crash to defeat.

The USA tinkered with their line-up for the game, with only two starters from the first game -- Donovan Mitchell and Myles Turner, with Los Angeles Lakers' Kyle Kuzma ruled out with a sore ankle.

In contrast Australia stuck with the same five, led by Mills and Bogut.

The five-time world champions hit their first points within 20 seconds and with good offence and finishing hung on to their lead, ending the first quarter with a 26-23 advantage.

But quick points at the re-start from Bogut drew Australia level and an Ingles three-pointer gave them the edge for the first time as shooting woes hit Team USA.

A seesawing second quarter saw them trade buckets before a late two-pointer from San Antonio Spurs' Derrick White gave the Americans a 49-48 first-half lead.

As they did in their match on Thursday, the USA lifted in the third quarter and raced 10 points clear.

But back-to-back threes from Mills closed the gap and two late free throws from Chris Goulding remarkably sent the Boomers into the final quarter with a 78-76 lead.

With the record crowd roaring them on, Australia took control as the clock ticked down to close an epic victory in their final game before heading to China.

Team USA have one more warm-up game left, against Canada in Sydney on Monday.