A Japanese skateboarder claimed a piece of Olympic history as the host nation enjoyed a gold rush at the Tokyo Games on Sunday, while France inflicted the first defeat on a men's USA basketball team since Athens 2004.

There were 18 gold medals up for grabs, including the first ever in skateboarding, one of several new sports introduced in Tokyo in a bid to attract younger fans.

A perfectly scripted final saw Japanese world champion Yuto Horigome strike gold.

US gymnast Simone Biles practises at the Tokyo Olympics
US gymnast Simone Biles practises at the Tokyo Olympics AFP / Loic VENANCE

The 22-year-old, who grew up just a stone's throw from the Olympic venue, landed three huge tricks in a row to eclipse American favourite Nyjah Huston, who finished seventh.

"This is special because it was held in Koto City, where I was born," said Horigome.

Horigome's victory was one of four golds Japan won on Sunday to take the host nation to second in the medals table behind China.

The haul included brother and sister Uta and Hifumi Abe both winning Olympic titles within an hour of each other.

Brazil's Italo Ferreira rides a wave during a training session at the Tsurigasaki Surfing Beach
Brazil's Italo Ferreira rides a wave during a training session at the Tsurigasaki Surfing Beach POOL / Olivier MORIN

Uta Abe was first to strike gold in the women's under-52kg category, beating Amandine Buchard of France.

She then cheered on as her big brother Hifumi overpowered Georgian judoka Vazha Margvelashvili in the under-66kg gold medal fight.

Earlier, unheralded swimmer Yui Ohashi had sparked the Japan gold spree in an action-packed morning session at the pool.

Japanese tennis star Naomi Osaka carries the Olympic torch
Japanese tennis star Naomi Osaka carries the Olympic torch AFP / Jeff PACHOUD

Ohashi powered to victory in the women's 400 individual medley, toppling Hungary's defending champion Katinka Hosszu.

"I swam believing in myself. I really did not think of winning the gold," said Ohashi.

A USA men's basketball team lost at an Olympics for the first time since the 2004 Athens Games as a team led by 11-time NBA All-Star Kevin Durant were beaten 83-76 by France.

Durant was held to just 10 points in an upset that shows the Americans have a fight on their hands to retain their title.

Japan's Yui Ohashi whose previous best performance on the world stage was a silver medal at the 2017 World Championships, touched in 4:32.08 ahead of US duo Emma Weyant and Hali Flickinger
Japan's Yui Ohashi whose previous best performance on the world stage was a silver medal at the 2017 World Championships, touched in 4:32.08 ahead of US duo Emma Weyant and Hali Flickinger AFP / Odd ANDERSEN

NBA player Evan Fournier top-scored with 28 points for France, finding form from three-point range late in the game to help his team claw back a 10-point deficit to stun the Americans.

Tunisian teenager Ahmed Hafnaoui pulled off the day's biggest swimming surprise by winning the men's 400m freestyle.

US gymnast Simone Biles has not lost an all-around competition since 2013, an eight-year spell that has encompassed 19 world championship titles and four Olympic golds
US gymnast Simone Biles has not lost an all-around competition since 2013, an eight-year spell that has encompassed 19 world championship titles and four Olympic golds AFP / Loic VENANCE

The 18-year-old had only qualified eighth-fastest for the final but produced a devastating late burst to win in 3min 43.36sec, overhauling Australian Jack McLoughlin.

"I just can't believe that, it's amazing," Hafnaoui said. "I felt better in the water this morning than yesterday and that's it. I'm the Olympic champion now."

It was just Tunisia's third gold ever in swimming.

The other swimming medals were split between the US and Australia, with Chase Kalisz winning the 400m medley and Australia taking gold in the women's 4x100m freestyle relay in a world record 3:29.69.

The upsets extended beyond the pool later Sunday, with Australian world number one Ashleigh Barty crashing out in the first round of the women's tennis singles. The reigning Wimbledon champion lost 6-4, 6-3 to Spain's Sara Sorribes Tormo.

Austrian mathematician Anna Kiesenhofer claimed a surprise victory in the women's cycling road race, which ended in bizarre fashion with Dutch veteran Annemiek van Vleuten crossing the line mistakenly thinking she had won.

Van Vleuten was oblivious to the fact that Kiesenhofer had broken away from the peloton to take gold.

"I'm gutted about this, of course," Van Vleuten said. "At first I felt really stupid, but then the others (her teammates) also did not know who had won."

Elsewhere on Sunday, a century-long wait to see surfing at the Olympics came to an end at Tsurigasaki Surfing Beach.

It marked the culmination of efforts to get surfing added to the Olympic programme dating back more than 100 years.

The spectre of Covid-19 meanwhile continued to stalk the Olympics, with the men's golf tournament upended by two high-profile withdrawals.

World number one Jon Rahm was ruled out after returning a positive test -- his second Covid-19 positive in two months -- while Bryson DeChambeau also saw his Olympic hopes end with a positive case.

In gymnastics, US superstar and defending champion Simone Biles produced a rusty performance in qualifying, with several uncharacteristic mistakes in a near-empty arena.

Biles rolled her eyes after one unsteady landing on the vault and had her performance director Tom Forster shaking his head in disbelief after a shaky end to her beam routine.

"Simone took three big steps on the beam dismount, I've never seen her do that before," said Forster.

"This is not the finals, this is getting into the finals, this might be a great awakening for us," he said.

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