Japan topped the medals table at the Tokyo Olympics after the host nation won three golds on Monday and British diver Tom Daley was finally crowned an Olympic champion at his fourth Games in an emotional triumph.

Heading the Japanese charge was 13-year-old skateboarder Momiji Nishiya who took gold a day after the host nation also won the men's title.

"I'm so glad to become the youngest (Japanese gold medallist) at my first Olympics... tears came to my eyes," Nishiya said.

Shohei Ono, one of Japan's biggest judo stars, won his second straight Olympic title with a tense victory over Georgian world champion Lasha Shavdatuashvili at the Nippon Budokan, the spiritual home of the sport.

US swimmer Katie Ledecky trains at the Tokyo Aquatics Centre US swimmer Katie Ledecky trains at the Tokyo Aquatics Centre Photo: AFP / Attila KISBENEDEK

Japan's third gold, and eighth of the Games so far, came in a table tennis shock as mixed doubles pair Jun Mizutani and Mima Ito claimed their country's first ever Olympic title in the sport.

China had won every Olympic table tennis gold medal since the 2004 Athens Games, but Xu Xin and Liu Shiwen blew a two-game lead in a thrilling final.

Tears flowed at the diving venue as Britain's Daley claimed a surprise first Olympic gold in the synchronised 10m platform event with Matty Lee.

The 27-year-old Daley is hugely popular in Britain, where he has spent half of his life in the public eye and become an LGBT figurehead.

US swimming star Caeleb Dressel US swimming star Caeleb Dressel Photo: GETTY IMAGES NORTH AMERICA / Maddie Meyer

His Olympic journey began as a 14-year-old at the 2008 Beijing Games and he won bronzes at the 2012 and 2016 Rio Olympics, but a gold medal had remained frustratingly elusive.

However on Monday, Daley and Lee capitalised after a rare blunder by China's Chen Aisen and Cao Yuan to snatch gold.

A tearful Daley paid tribute to late father Rob, who died of cancer in 2011 at the age of 40.

Norway's Kristian Blummenfelt celebrates his gold medal in the triathlon at the Tokyo Olympics Norway's Kristian Blummenfelt celebrates his gold medal in the triathlon at the Tokyo Olympics Photo: AFP / Loic VENANCE

"He never saw me win an Olympic medal, get married, have a child, teach me to drive, have a pint down the pub," said Daley.

"He took me to every training session, every competition, he was always there."

Elsewhere Monday, the battle for supremacy between swimming superpowers Australia and the United States heated up.

Ariarne Titmus landed the biggest blow for Australia with a pulsating victory over American great Katie Ledecky in the 400m freestyle.

Caeleb Dressel (right) and Blake Pieroni celebrate victory for the United States in the 4x100m freestyle relay Caeleb Dressel (right) and Blake Pieroni celebrate victory for the United States in the 4x100m freestyle relay Photo: AFP / Jonathan NACKSTRAND

Ledecky came to Japan on the back of winning four gold medals and a silver at Rio in 2016, but Titmus ousted her as world champion in 2019 and topped the timesheets this season.

The Australian reeled in Ledecky over the final 50m and said afterwards: "To pull it off in the backend against someone who has an amazing second half of her race, I'm really proud of that."

The United States bounced back to claim an emphatic victory in the men's 4x100m freestyle relay. Zach Apple brought them home after Caeleb Dressel led off, ensuring they touched in 3:08.97, ahead of Italy and Australia.

Despite her setback, Ledecky was back in the pool in the evening to post the quickest time in the 200m heats and qualify fastest for the 1500m final.

In gymnastics, the Russian team claimed their first men's team gold since the 1996 Atlanta Games as they stormed past defending champions Japan and left China in bronze medal position.

The outcome of the first gymnastics gold on offer was in the balance right until the closing exercise when reigning world all-around champion Nikita Nagornyy secured the gold with a superb score on the horizontal bar.

Britain's unstoppable Adam Peaty extended his dominance of the 100m breaststroke, powering to gold in 57.37sec ahead of Dutchman Arno Kamminga to retain his 2016 Olympic crown.

Tom Pidcock won the mountain bike cross-country title for Britain's third gold of the day.

Day three's action got under way with chaotic scenes at the men's triathlon, eventually won by Norway's Kristian Blummenfelt.

In a farcical false start, around two-thirds of the 56 competitors dived into the water and set off on the swimming leg only to be hauled back.

The bungled start was caused by a media boat filming the competitors before they dived in for the swimming leg.

Japan's tennis favourite Naomi Osaka eased into the third round of the women's singles with a 6-3, 6-2 win over Switzerland's Viktorija Golubic.

In the men's event, world number one Novak Djokovic beat Jan-Lennard Struff of Germany 6-4, 6-3 to stay on course for a first Olympic title.

NBA star Luka Doncic made a sensational Olympic debut, hitting 48 points as Slovenia routed Argentina 118-100.

"It was very special," Doncic said. "Both for me and the whole team."

Covid-19 continued to stalk the Games however, with Dutch tennis players Jean-Julien Rojer and Wesley Koolhof pulling out of the men's doubles after Rojer tested positive for coronavirus.