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.
World record-holder McIntosh produced a dominant 400m medley swim in Paris, clocking the fourth-fastest time ever.
But the US sprint king tipped to be one of the faces of the Paris Games said Monday that his growing fame has become a problem in the Olympic Village.
The 54-year-old businesswoman had not missed a Summer Games since 1992 until a pandemic-enforced spectator ban meant she had to watch an Olympics taking place in her home city on TV.
It was 24-time Grand Slam champion Djokovic's 31st win in a rivalry which began on the same Roland Garros clay courts in 2006.
The cauldron flies into the Parisian sky at sunset each day under a 30-metre balloon in the Jardin des Tuilleries park.
The quality and quantity of food drew criticism from athletes after catering staff rationed breakfast eggs last week.
The 19-year-old Chinese won with an Olympic record aggregate of 252.2 to finish ahead of Sweden's Victor Lindgren, who scored 251.4 to take the silver medal.
Ban, 16, topped Sunday's qualification with an Olympic record total but her late wobble allowed Huang, 17, to draw level at 251.8, forcing a shoot-off between the teenagers.
In a joint statement, Paris 2024 organisers and World Triathlon said they had taken the decision to cancel Monday's swimming training session because "water quality levels... do not present sufficient guarantees" to allow it to take place.
The United States captured bronze in the men's gymnastics team final at the Paris Games on Monday, ending a 16-year Olympic medal drought thanks to a bounce-back performance from Brody Malone.