Norway's Karsten Warholm produced a devastating performance to smash his own world record and win the Olympic men's 400 metres hurdles gold on Tuesday.

Touted as one of the stand-out events of the 10-day track and field programme at the Olympic Stadium, the cream of a very good hurdling crop did not fail to deliver in a thrilling race despite stifling midday heat and humidity in Tokyo.

Warholm clocked a remarkable 45.94 seconds, pulverising his previous world best of 46.70sec. To put that performance into perspective, only four runners in history have even clocked sub-47sec times, let alone sub-46.

American arch-rival Rai Benjamin won silver in 46.17sec, with Brazil's Alison Dos Santos claiming bronze in 46.72, both regional records that also smashed their previous personal bests.

As the Norwegian, with minimum upper body movement as he negotiated the early hurdles, hit the final 200 metres well ahead of the field, the question was whether he could keep his rhythm and pace.

Benjamin had not given up hope and pushed down the home straight, coming almost neck-and-neck on the 10th and last hurdle.

Warholm, teeth gritted and head flailing, looked like he might tie up to hand the American victory.

But from somewhere, the Norwegian two-time world champion dug deep and found just enough energy for an extra spurt that saw him surge through the line.

Eyes bulging at the world record time flashed up on the big screen, Warholm roared and spontaneously ripped open his shirt amid gasps from sparse pockets of fellow athletes and team officials at a stadium empty of spectators because of coronavirus rules.

There were national records for British Virgin Islands' Kyron McMaster in fourth, Turkey's Cuban-born 2017 world silver medallist Yasmani Copello in sixth and Estonian Rasmus Magi in seventh.

Qatar's 2019 world bronze medallist Abderrahman Samba, one of the four runners to have dipped under 47 seconds in his career, was fifth in a season's best of 47.12.

The result caps a remarkable renaissance of the event, both for men and women.

The breakthrough for Warholm came at the Oslo Diamond League last month.

On his home track of Oslo on July 1, the 25-year-old timed 46.70sec to break Kevin Young's long-standing mark set at the 1992 Barcelona Olympics, almost four years before he was born.

That result had come just days after Benjamin ran a world-leading 46.83sec to win the US Olympic trials.

There were similar upheavals in the women's 400m hurdles when American Sydney McLaughlin became the first woman to dip below the 52-second mark.

McLaughlin clocked 51.90sec to also win the US trials last month after a superb tactical race against reigning Olympic and world champion Dalilah Muhammad.

The women's final, featuring McLauglin and Muhammad, is set up nicely for Wednesday.

US sprinter Felix off the mark at farewell Olympics

Allyson Felix made a smooth start to her quest for a record-breaking 10th Olympic medal on Tuesday, strolling to a comfortable win in the opening heats of the 400m. 

The 35-year-old queen of US track and field, competing in her fifth Olympic Games, cruised through her heat in 50.84sec, the fourth fastest time of qualifying.

Felix is the only female track and field athlete in history to win six Olympic gold medals and is currently tied with Merlene Ottey on nine medals as the most decorated female Olympian in track and field history.

"It's nice to get going," Felix said after her win. "It feels like I've been waiting forever. It felt good to get out there and bump it up for the semi."

Felix, who plans to retire before the 2024 Olympics, said she was cherishing her final appearance on the Olympic stage, which she first graced as a teenager in Athens in 2004.

"Obviously I love this sport," she said. "It's been so much of my life and I think that's why, knowing this is my last time around it means a lot to me."

Felix, a silver medallist in the 400m in 2016, is racing in her first Olympics as a mother.

She gave birth to daughter Camryn in 2018 after an emergency C-section and has since been a vocal advocate for the rights of working mothers.

"It's changed everything," Felix said of motherhood. "It's given me a different drive. I've had so many challenges because of it. So I think it's even more meaningful now to be on this stage as a mom."

Felix split with her long-time sponsors Nike in 2019 after criticising the sporting apparel giant for seeking to slash her pay after she became pregnant.

She has subsequently launched her own line of footwear and running shoes, which she wore proudly on Tuesday in the Olympic Stadium.

"I feel so proud for what we stand for, and what we're building and for focusing on women who for far too long have been overlooked," she said.

Felix is almost certain to pull clear of Ottey as the most decorated Olympian in her final Games. As well as the 400m, she will most likely race in the 4x400m, an event the US has dominated for decades, and may also feature in the 4x100m relay.

Irie becomes Japan's first woman champion in Olympic boxing
Sena Irie became the first Japanese woman to win Olympic boxing gold on Tuesday, defeating Nesthy Petecio of the Philippines on unanimous points to take the featherweight title in Tokyo.

It was disappointment for Petecio, who had been looking to earn the Philippines' first Olympic gold in the country's proud boxing history.

Judges' scorecards -- which are now displayed after each round to make Olympic boxing more transparent -- unanimously had the 20-year-old Irie ahead after round one.

Both boxers were letting their fists go in a lively and open contest at Kokugikan Arena, which is usually used for Japan's national sport, sumo.

The 29-year-old Petecio, the 2019 world champion, had the better of the second round. 

The third was also highly competitive, but it was Irie who got the nod from the judges, putting her hand over her mouth and crying.

The Philippines are still in contention for another gold, with Carlo Paalam facing another Japanese fighter, Ryomei Tanaka, in the men's flyweight semi-finals on Thursday.

Paalam, who is now guaranteed at least bronze, defeated Shakhobidin Zoirov of Uzbekistan in his quarter-final Tuesday.