De Grasse, who took silver behind Usain Bolt in this event at Rio 2016, ran a superb technical race to finish strongly in a national record of 19.62sec.

Kenny Bednarek won silver in a personal best of 19.68, while Lyles - who has not run at the top of his form this year - had to settle for bronze in 19.74.

Five years ago Bolt said of the then 21-year-old De Grasse, who, as he did here, also won 100m bronze in Rio: "He's going to be good, he runs just like me, I mean he's really slow at the blocks but when he gets going, he gets going."

Finally De Grasse, whose career has been undermined by serious hamstring injuries, has had the opportunity to prove the retired Jamaican legend's judgement correct.

He had promised much after qualifying fastest in a national record of 19.73, and tonight De Grasse delivered with a cool and disciplined display of sprinting.

The third US runner home was 17-year-old Erriyon Knighton, earning a superb fourth place in 19.93.

But Canada are back at the top of the men's sprinting world for the first time since Donovan Bailey won the world and then Olympic 100m titles in 1995 and 1996.

"I've been waiting for this moment, I've been training hard for this moment," De Grasse said.

"I went back after the 100m and I was a little bit disappointed in myself, that I could have done better. 

"I said, 'I gotta go and get this 200, I gotta go and get it'.

"I knew the Americans were going to push me, and they were going to take me to a personal best. 

"It's been five years since I had a personal best, so it was just good to get that finally out the way."

Earlier in the evening Peruth Chemutai won the women's 3,000m steeplechase for Uganda - thus becoming the country’s first female Olympic champion - in a national record of 9min 1.45sec after hunting down and passing the leader at the bell, Courtney Frerichs.

The American, who won world silver in 2017, made a bold break with three laps to go and while she was passed in the back straight, Frerichs held off the challenge of Kenya's 2015 world champion Hyvin Kiyeng over the final 30m to earn another global silver in 9:04.79.

"I am feeling great," said Chemutai.

"Today I made it - it is the first time Uganda gets the gold medal in 3,000m steeplechase. 

"I am so happy to be an Olympic champion."

Kiyeng took bronze in 9.05.39, with her compatriot, world champion and record-holder Beatrice Chepkoech, having to settle for seventh place after fading out of contention in the second half of the race.

It was not all frustration for Kenya, however, as they took gold and silver in the men’s 800m final thanks to Emmanuel Korir and Ferguson Rotich.

Korir won in 1:45.06 after chasing and passing the leader at the bell, Peter Bol of Australia, in the final straight.

The eventual gold medallist was rocking with effort as he crossed the line, just holding off the challenge of his faster-finishing team mate Rotich, who took silver in 1:45.23.

Patryk Dobek, Poland's European indoor champion, was the third runner to sweep past Bol - who arrived in Australia as a refugee from Sudan aged eight - in the closing stages, claiming bronze in 1:45.39.

Bol the bold was nearly rewarded for his efforts - but had to settle for fourth place in 1:45.92.

"This is a big thing for me after failing to qualify for the final in the 2017 and 2019 World Championships," said Korir. 

"But today is my day."

The only field final of the evening session on day six of the athletics programme saw Poland dominate the men’s hammer throw final, where Wojciech Nowicki - third at Rio 2016 and bronze medallist at the last three World Championships - at last got the global golden feeling thanks to a third-round best of 82.52 metres.

His team mate Pawel Fajdek, four times a world champion but unable to reach the Olympic final from qualifying at the London 2012 and Rio 2016 Games, broke through to win bronze with a fifth-round effort of 81.53m.

Silver went to Norway's Eivind Henriksen, who twice improved the national record in the final, finishing with a best of 81.58m.

"It was a dream for me for the two of us to be at the podium together," said Nowicki.

Fajdek commented: "For me this bronze medal is like a gold.

"Everyone knows what happened in London and Rio but now everything has changed. 

"Now I am an Olympic medallist, my mind will be free.

"Next year I will be better. 

"Next year I will try to break the world record."

Anouk Vetter of The Netherlands installed herself as overnight leader of the heptathlon after four of the seven events, producing the third-fastest time of 23.81sec in the concluding 200 metres.

In the opening heat, Britain’s world champion Katarina Johnson-Thompson, who required an operation for a ruptured Achilles tendon in December, hopped to a painful halt before doggedly jogging to the line - only to be disqualified for going out of her lane when she collapsed briefly to the track.

Johnson-Thompson had stood fifth after the 100m hurdles, high jump and shot put before she came to grief.

Vetter has 3,968 points, with Belgium’s Noor Vidts moving into second place overall on 3,941.

Vidts’s team mate Nafi Thiam, the defending champion, is third overall on 3,921 having finished 18th in the sprint in 24.90.

In the decathlon, Canadian Damian Warner finished as overnight leader on 4,722 points with 21-year-old Ashley Moloney of Australia second on 4,641.

World record-holder Kevin Mayer from France, who said earlier in the day that a back injury he had sustained since arriving in Japan meant he could not compete without pain, stands fifth overnight on 4,340.

World champion Niklas Kaul did not finish the 400m and left the Olympic Stadium in a wheelchair.

Meanwhile Sifan Hassan of The Netherlands, who plans to add the women's 10,000m and 1500m titles to the version she has already won her over 5,000m, safely qualified for Friday's (August 6) 1500m final.