The 22-year-old Briton led Croatia's Matea Jelić by three points until the latter landed two head kicks that provided a stunning conclusion to the final.

Despairingly, Williams - who had beaten the gold medal favourite, Rio 2016 bronze medallist Ruth Gbagbi of Ivory Coast, in the semi-final - surged forward in the last three seconds in an effort to counter-attack.

But it was too late - the score remained at 25-22 and gold went to Jelić.

Williams, who had been hoping to emulate her Welsh compatriot Jade Jones, who she had watched on TV winning the first of her two Olympic titles at the London 2012 Games - collapsed motionless on the edge of the mat.

"It's not enough, I know it's not enough," she said. "I had her with 10 seconds to go, but I messed up and that's on me. I knew I was winning, but I didn't know there was only 10 seconds left.

"I made a mistake and she reacted and I've got to accept that and move on. It was a mental block. It happened on the biggest stage of my career, that's a hit, but hopefully it will never happen again."

She added: "An Olympic silver medal, it's not bad, is it?"

Her achievement was all the greater for the fact that her preparations for the delayed Olympics had been disrupted by a torn right hamstring three weeks before competition began, as well as flight delays which meant she had arrived late at her pre-Games training camp.

"It's been tough, physically and mentally, over the last few years with all the injuries I've had," she said. "And the flight was delayed coming out here, so it hasn't been easy. But there is no excuse."

Williams was world youth champion in kickboxing by the time she watched Jones - who is now a training partner - winning at the London Olympics. She was signed up for trials in taekwondo by her father.

Having been selected aged 14, Williams was not old enough to enter the athlete accommodation at the team's base in Manchester. Instead, her mother quit her job, and the two of them lived in a caravan near the site. They stayed there for 18 months.

Such was the commitment of Williams' parents that they flew to Rio in 2016 even though their daughter was only a reserve in the British team there.

While they were not able to be in Tokyo, they have witnessed numerous triumphs over the past eight years.

Williams announced her enormous potential by winning the world youth title in Taipei in 2014, and two years later she was European senior champion in the under-67kg category at the age of 17. Later that year she retained her world youth title…

She also retained her European title at the 2018 Championships in Kazan, and earned it a third time in the following year's Extra European Championships in Bari before losing the title last year after a 13-10 defeat by Jelić.

Her performance at the 2017 and 2019 World Championships was relatively disappointing - but Tokyo 2020 underlined her ability to make a big splash in global competition. Expect more water to be displaced imminently…