The Netherlands had reason to celebrate and cause for concern at the Izu Cycling Centre on Thursday, while Great Britain's Matthew Walls stormed to victory in the omnium.

Olympic debutant Shanne Braspennincx capped an incredible comeback from a heart attack six years ago to take gold in the women's keirin final, as the Netherlands defended the title Elis Ligtlee won in Rio 2016.

However, her triumph came after team-mate Laurine van Riessen had crashed out in the quarter-finals, taking Team GB's Katy Marchant with her.

Van Riessen was knocked unconscious and had to be taken off the track on a stretcher before she was transferred to hospital for further checks.

"Coach Hugo [Haak] said that our team doctor is with her. I sent her a message but it all went so fast and I had to go on," Braspennincx said when asked about Van Riessen's injury.

"Hugo does that. He told me she's in good hands; you have to focus on your own race now. I was worried about her, she went to the hospital, but at that moment I had to make the switch and focus on myself.

"It's tough to see. I know it's part of [racing] but this is what you really don't want and she was in very good shape as well."

Van Riessen clipped the wheel in front of her as she was about to enter the final lap, sliding straight into the unfortunate Marchant in the process.

"I think that’s just bike racing, wrong place, wrong time, I just hope everyone's okay that was in the crash. I think I'm okay, just a bit battered and bruised but I'm alright," Marchant told BBC Sport.

"I needed to finish the race in case there was something that came up on the results. I'm not really sure what happened, wrong place, wrong time, I just got caught up it in it."

A SURREAL SUCCESS

Braspennincx's triumph is made even more remarkable by the heart attack she suffered in 2015.

The Netherlands have now won the women's keirin event on two of the three times it has been held at the Olympic Games, and it brought up the nation's 10th gold medal on the track.

She finished ahead of Ellesse Andrews – the second woman from New Zealand to win an Olympic medal in the velodrome after Sarah Ulmer in 2004 – and Canada's Lauriane Genest.

"I'll have to let it sink in first, it feels surreal," Braspennincx said. "I can't believe it. I don't know what it was like. I went in the moment, I had to go and I held it.

"I think every athlete can say it's a very long [journey], especially this one. In Rio I was a spare rider because I had an injury. I had a long way to come back, and to celebrate it like this is worth it.

"There is amazing medical stuff still behind me. They tested me through, through and through in order to get the green light. In January 2016 I got to be an athlete again. My journey started again, really, really slow, and with a lot of stuff back. And now I am here in 2021, all good."

TEAM GB'S WONDER WALLS

Despite Marchant's disappointment, there was joy for Team GB in the men's omnium, as 23-year-old Olympic debutant Walls claimed gold in dominant fashion.

Walls, who tested positive for COVID-19 in March, accumulated 153 points across the four disciplines – with the entire event condensed into the space of three hours – to finish ahead of Campbell Stewart and defending champion Elia Viviani.

It brought up Team GB's first track cycling gold at Tokyo, adding to their successes in the BMX and mountain biking events.

Team GB have now won 16 golds and 50 medals overall at the close of racing at the velodrome. Ed Clancy (2012) and Mark Cavendish (2016) have previously taken bronze and silver in the men's omnium, while Laura Kenny goes into Sunday's women's event as the two-time defending Olympic champion.

"I managed to get a good lead coming into the end. It's been a hard day but I came into that points race with a bit of a lead and breathing room," Walls told BBC Sport.

Britain are the first nation to win three Olympic medals in the men's omnium, while Team GB have now won gold in nine of the current 12 events held on the cycling track at the Games.

Stewart's silver, meanwhile, means New Zealand have taken 19 medals in Tokyo, surpassing their record tally of 18, set five years ago in Rio.

WORLD CHAMPION LAVREYSEN ENDS KENNY'S DEFENCE

Jason Kenny's defence of his Olympic gold in the men's sprint came to an end as he was overcome by Dutch world champion Harrie Lavreysen.

Kenny took gold in London and Rio, but the 33-year-old's reign is now over, and Lavreysen looks good to push on for the biggest prize.

The Dutchman was pushed hard in his two races against Kenny, however, with the Team GB rider forcing a two-lap sprint in the second quarter-final heat before Lavreysen pulled away on the final turn.

Lavreysen must get past another Briton in the semi-finals, with Jack Carlin up next.

Carlin looked sharp and showed complete control in his quarter-final win over Maximilian Levy of Germany.

"Another day in the bag, see what happens tomorrow but the legs are feeling good, it's all to play for tomorrow," Carlin told BBC Sport.

"My legs are feeling alright, they're sore but everyone's are sore at this point of the week. I think we take each race as it comes, stick to our principles, keep calm and what will be, will be."

Asked about Kenny's valiant effort, Carlin added: "I think you saw today he was struggling a bit from fatigue. He still went out there and gave it his all, that's what Olympic champions do."

The other semi-final will see Denis Dmitriev face the Netherlands' Jeffrey Hoogland, meaning the Dutch are guaranteed a medal.