The United States saw a 25-game winning streak in men's basketball at the Olympics come to an end as they were beaten by France in their first outing at Tokyo 2020.

Team USA arrived in Japan looking to strike gold for a fourth straight Games, yet their build-up had been anything but straightforward. Exhibition defeats to Australia and Nigeria raised concerns before traveling, while COVID-19 protocols ruled out Bradley Beal and Kevin Love was replaced at late notice by JaVale McGee.

Still, a squad including Kevin Durant, Damian Lillard and Jayson Tatum – as well as Khris Middleton and Jrue Holiday from the Milwaukee Bucks, the newly crowned NBA champions – saw the reigning champions listed as favorites.

France, though, caused an early upset at the start of the tournament. Evan Fournier starred with 28 points to help his team triumph 83-76 at the Saitama Super Arena.

There were wins for Australia and Italy too on Sunday, as well as a victory for the Czech Republic.

Big names come up short in shock defeat

Team USA had rounded out their build-up to the Games by beating Spain, yet there will be concerning signs for head coach Gregg Popovich following a flat performance against France.

They were successful with just 41 per cent of their two-point attempts and landed only 10 of the 32 shots put up from beyond the arc. Despite the shooting issues they still led 45-37 at half-time, only for the game to turn in a third quarter where they mustered a paltry 11 points.

Durant finished up with 10 points on 4-of-12 shooting, while Lillard had 11. The latter's slip that caused a turnover in the closing seconds when down by four rather summed up a disjointed performance from the entire roster, leading to a first loss at the Olympics since going down to Argentina at Athens 2004.

Devin Booker, who had helped the Phoenix Suns reach the NBA Finals, landed only one of his six attempts from the field, with Holiday (18 points) finishing as the USA's leading scorer having only joined up with the team on the day of the game.

Also in Group A, the Czech Republic recorded an 84-78 victory over Iran.

Ingles impressed, but Nigeria come up short

Nigeria had defeated both Argentina and the United States ahead of the Games, raising hopes of making an impact in Japan.

However, able to knock down just 29 per cent of their attempts from deep, they struggled to keep pace with Australia, scoring only 27 points in the entire second half as they went down 84-67.

Still, Joe Ingles – who had 11 points for Australia – praised the Nigerians for their display, particularly on defense as they forced 21 turnovers. Patty Mills was the leading scorer in the game, finishing with 25.

"You have to give a lot of credit to Nigeria, with how they played and the style they play," Ingles said. "They are up and in, they are athletic and get up the floor, and they obviously have a great coach [in Mike Brown].

"I think a lot of people underestimate the team and the country. They are a really good basketball team."

Meanwhile, Italy opened their Group B campaign with a 92-82 victory over Germany. Simone Fontecchio led the way with 20 points, including landing all five of his three-point attempts.