It was the sixth time McLaughlin-Levrone had broken the world record, lowering her previous mark of 50.65 set at the U.S. trials in June.
Lyles, who had been bidding to complete a 100m-200m double in Paris, was taken off the track in a wheelchair following the race, won by Botswana's Letsile Tebogo.
The 26-year-old, who had claimed virtually every other title in an utterly dominant half decade including three world championship gold medals, clocked 12.99 seconds.
A tense game ended all square at 1-1, with fourth-quarter goals in quick succession from Dutch captain Thierry Brinkman and Germany's Thies Prinz.
Nadeem threw an Olympic record of 92.97 metres for victory, India's defending champion Neeraj Chopra taking silver with 89.45. Grenada's Anderson Peters claimed bronze with 88.54m.
Marathon swimming is set to get underway amid concerns over water pollution in the river Seine.
There will be 21 medals up for grabs with the bulk of them being given out in athletics.
"The last hurrah, I'm done. I've always said I want to retire a champion, that's it," Harrington told Irish national broadcaster RTE.
Alfred is seeking to emulate Jamaica's Elaine Thompson-Herah, who did the 100m-200m double at the Rio 2016 Games and at the Covid-delayed Tokyo Olympics.
"The Chinese train so hard, the way that they train, everything is close to perfection," the Briton said.
"I'm soaking wet, honestly," he said. "It's a very, very humid day as it was yesterday. I just hope it rains so it cools down the temperature a bit and the air," said Djokovic.
"I can't find the words, it's crazy what's happening to me. This morning, I would never have believed it," Beaugrand said.
Nuclear-armed North Korea declared the South its principal enemy earlier this year and tensions between the two countries are at one of their highest points in years.
Five medals will be on offer in the swimming at La Defense Arena, including the men's 100 metres freestyle, 200 butterfly, 200 breaststroke and the women's 100 freestyle.
Adding to the early criticism about the quality and quantity of the food at the Olympic Village, the queen of gymnastics gave the French offerings there a thumbs-down, opining that athletes would need to get out to enjoy the "real" local cuisine.
The men's and women's triathlons were given the green light a day after the men's event had been postponed because of pollution levels in the Paris waterway.
On Tuesday, McKeown retained her 100m backstroke crown from Tokyo, crushing American rival Regan Smith to earn her fourth Olympic gold medal and join a select group of swimmers with three individual titles.
Some Christian groups and conservative politicians have said they were angered by a segment of the opening ceremony showing a kitsch scene which appeared to parody Leonardo da Vinci's famous "Last Supper" painting of Jesus Christ and his disciples.
All four sides in Group B were tied on three points going into the last matches, but Javier Mascherano's Argentina qualified by beating Ukraine 2-0 in Lyon while Morocco eased through with a 3-0 victory against Iraq in Nice.