France's Leon Marchand created history in front of a wild home crowd with a golden double, while American Katie Ledecky won a record-equalling eighth Olympic gold medal on an epic night of swimming in Paris.
In an remarkable, ear-splitting atmosphere, Marchand achieved the rare feat of winning two golds in the same swimming session.
The 22-year-old first reeled in reigning champion and world record holder Kristof Milak of Hungary to win the 200m butterfly title and, less than two hours later, returned to the pool to cruise to victory in the 200m breaststroke and secure his third gold of the Games.
No-one had previously completed the men's 200m butterfly-breaststroke double and Marchand won both in Olympic-record times.
In becoming the first swimmer to win two individual golds in one night at the Olympics since 1976, the poster boy of these Games cemented himself as a global superstar of the sport.
"When you talk of Michael Phelps, when you talk of Ian Thorpe, you are now going to have to talk about Leon Marchand because that is one of the best things I think we have ever seen," British Olympic champion Adrian Moorhouse said on BBC TV.
Earlier, 27-year-old Ledecky, who achieved such iconic status long ago, dominated her rivals to retain her 1500m freestyle title in an Olympic record time - and equal compatriot Jenny Thompson as the most successful female swimmer in Games history.
It was Ledecky's 12th medal overall, which gave her an identical record to Thompson, whose haul of eight golds, three silvers and one bronze came between 1992 and 2004.
And, to cap off a stunning session of swimming, Pan Zhanle of China won the 100m freestyle in a world record time of 46.40 seconds, refusing to be forgotten in what is usually the sport's blue-riband event.
The 15,000-capacity indoor arena has already been dubbed the loudest and best swimming venue in recent memory. Tickets to see Marchand, from Toulouse, have been the hottest property in town.
This, though, was something else - each of Marchand's strokes in the breaststroke leg met with huge roars of "Allez" by a crowd who had turned up with flags, horns and masks of their hero.
His first victory, in a time of one minute 51.71 seconds, was gripping. He trailed by almost a body length at the final turn but overhauled Milak, regarded as the greatest butterfly racer in history, in the final strokes with the crowd on its feet.
Marchand had his first medal ceremony before his next final but, rather than joining Milak and bronze medallist Ilya Kharun of Canada on a lap of honour, he disappeared quickly to recover.
He then completed a pure procession, winning in 2:05.85 to beat Australia's defending champion Zac Stubblety-Cook by almost a second, and the praise soon poured in on social media.
French president Emmanuel Macron labelled him the "merchant of dreams" and a "legend", while World Cup-winning footballer Antoine Griezmann called Marchand the "Little Prince of the Pool".
Marchand has been the rising star of swimming since sending US great Phelps' former coach Bob Bowman a letter, asking to be taken under his wing – a request duly accepted by the much-revered American.
Last year Marchand, known in Japan as 'the new monster', broke Phelps' last remaining world record in the 400m medley which confirmed his status as an elite all-rounder.
He won the 400m medley title here on Sunday too, but in these wins on Wednesday, for which the schedule was altered to allow him the chance of further glory, he beat specialists of their stroke.
"A double Olympic champion in one session - not even Michael Phelps tried that," said BBC commentator and former Olympic swimmer Andy Jameson.
"The audacity. I cannot believe he even tried it, never mind won them both."
The night ended with a final rendition of the French national anthem but it felt like the party would go on long into the night.
Marchand will have a day off on Thursday before returning for his fourth event on Friday - the 200m medley, where he will compete against Britain's Tom Dean and Duncan Scott.
Ledecky, who has revolutionised distance swimming, was seven seconds quicker than Tokyo, leading to belief the American is, somehow, getting even better.
When she won in Paris with a time of 15 minutes 30.02 seconds there was not another swimmer in sight on the TV pictures.
Ledecky won her first gold at London 2012 as a 15-year-old and followed with four more in Rio de Janeiro, before another two in Tokyo. Only Phelps has won more swimming golds than her.
The 27-year-old will also compete in the 800m freestyle on Friday, an event in which she is the three-time Olympic champion and world record holder.
Another victory would mean Ledecky equals the record of gymnast Larisa Latynina – the most successful female Olympian in any sport. She won nine golds for the Soviet Union in the 1950s and 1960s.
