US gymnastics star Simone Biles launches her bid for Olympic immortality at the Tokyo Games on Sunday as surfing and skateboarding make their debuts as part of a drive to attract young audiences.

American swimmer Chase Kalisz won the first of 18 gold medals up for grabs on day two of the Games as Japanese tennis star Naomi Osaka prepared to return to the court after her self-imposed exile.

The Ariake Gymnastics Centre will be the setting as Biles, 24, starts her bid to become the first woman in more than half a century to retain the all-around title.

The American could leave Tokyo with a career haul of nine Olympic gold medals, equalling the record set by Soviet gymnast Larisa Latynina in Tokyo in 1964.

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.

In acknowledgment of her domination, Biles has been awarded her own emoji on Twitter — a goat in a leotard symbolising her status as the GOAT, or greatest of all time.

Surfing and skateboarding are part of four new sports in Tokyo, along with karate and sport climbing.

The inaugural men’s surfing competition got under way in bright sunshine at Tsurigasaki Beach, 100 kilometres (60 miles) east of Tokyo.

Brazil’s Italo Ferreira, who learned to surf standing on the foam boxes his father sold fish from, will start as one of the favourites, with Japan’s Kanoa Igarashi another big name.

“I’m so stoked. It’s a special event,” said Ferreira, who finished first in his opening heat. “I’ve been training a lot in the last couple of months. I’m glad to be here and I think that was a good heat.”

The first Olympic skateboarding champion will be crowned, with America’s Nyjah Huston and Japan’s Yuto Horigome fierce rivals in the men’s street competition.

In the pool, Kalisz claimed gold in the men’s 400m individual medley for the United States while Japan’s Yui Ohashi won the women’s race.

Tunisian teenager Ahmed Hafnaoui upset the field to win the men’s 400m freestyle.

Australian Open champion Osaka has not played since May, when she walked out of Roland Garros saying that media commitments were harming her mental health.

But she appeared buoyant after lighting the Olympic cauldron on Friday, and will expect a warm welcome in Tokyo even if fans are barred because of coronavirus restrictions.

Firing up the cauldron was “undoubtedly the greatest athletic achievement and honor I will ever have in my life”, tweeted Osaka, who plays China’s Zheng Saisai in the first round.

World number one Ashleigh Barty, who won Wimbledon earlier this month, launches her campaign against Spain’s Sara Sorribes Tormo.

A formidable USA team led by Kevin Durant take on France in basketball, and Dutch two-time world champion Anna van der Breggen will target back-to-back golds in the women’s cycling road race.

Britain’s Jade Jones is bidding to become the first athlete to win three Olympic titles in taekwondo.