With firsts being made all over Paris on an action-packed day, a row over gender eligibility in boxing rumbled on as the Algerian in the spotlight boxed her way to a guaranteed medal.
Alfred conjured up a superb race in the Parisian rain to shock favourite Sha'Carri Richardson into silver with a time of 10.72sec in front of a raucous crowd at the Stade de France.
The 23-year-old was in tears of celebration after sealing a sensational win -- she had never finished on the podium at a major outdoor championships prior to Saturday's final.
"It feels amazing... it still hasn't sunk in," Alfred said.
There was also heartbreak for two-time 100m gold medallist Shelly-Ann Fraser-Pryce from Jamaica, who pulled out just before the semi-final, apparently injured.
The flamboyant Richardson was bidding for redemption three years since a positive marijuana test after her victory at the US trials wrecked her Olympic dreams in Tokyo.
'Nailed that one'
From one redemption campaign to another.
US gymnastics great Simone Biles clinched her third gold in Paris after famously imploding in Tokyo with the debilitating mental block known as the "twisties."
Her demons well and truly conquered, the 27-year-old Biles landed a stunning vault so difficult no other woman even attempts it.
"I kind of nailed that one," grinned Biles, who admitted she was tempted by her home Olympics in Los Angeles in four years but was not getting any younger.
More history was made at the gymnastics as Carlos Yulo from the Philippines snatched his country's second-ever gold, triumphing in the men's floor exercise.
Then Rhys McClenaghan captured Ireland's first-ever Olympic gymnastics medal with gold on the pommel horse.
Sensational summer
More history was made in the pool on the penultimate night of swimming as US legend Katie Ledecky powered to a fourth straight 800m freestyle title.
Her ninth career Olympic gold at the age of 27 equalled former Soviet-era artistic gymnast Larisa Latynina as the most decorated woman Olympian in any sport.
The greatest distance swimmer the sport has seen, she had already won the 1500m and earned silver in the 4x200m freestyle relay and bronze in the 400m freestyle in Paris.
Meanwhile, teen sensation Summer McIntosh enhanced her status as one of the Paris rising stars, taking her third gold in the 200m individual medley with an astonishing late surge.
Then the United States notched the second world record of the Olympic swimming competition, blasting to gold in the 4x100m mixed medley relay.
'It's a battle'
Off the field of play, a simmering scrap over gender in boxing was back in the spotlight as Imane Khelif overcame Hungary's Anna Luca Hamori on points to ensure at least a bronze medal.
The Algerian broke down in tears after the bout, which also saw the two boxers share an embrace.
"It's a battle, it's for my dignity," said Khelif, who brought "honour to Algeria, Algerian women and Algerian boxing," according to the country's president.
Khelif's 46-second victory over Italy's Angela Carini sparked a row that spilled beyond the ring, with politicians and celebrities weighing into the controversy.
The International Boxing Association disqualified Khelif at last year's world championship, saying she had failed an unspecified gender eligibility test.
There is no suggestion Khelif identifies as anything other than a woman - in fact, her father recently showed her birth certificate to AFP - and IOC president Thomas Bach called for an end to the scrap, that has also impacted Taiwan's Lin Yu-ting.
'I'm tired'
Earlier on the track, US sprint king Noah Lyles launched his campaign for men's 100m glory, recovering from a slow start to come through his heat.
The 27-year-old was one of the last out of the blocks in his heat but powered through the field, finishing second to Britain's Louie Hinchliffe in a time of 10.04sec.
Jamaica's Kishane Thompson looked in ominous form, running 10 flat but easing down significantly in the final stages.
Italy's Marcell Jacobs, who won a surprise gold in Tokyo, also laboured through his heat and just scraped through in a time of 10.05 sec.
The second full day of athletics in Paris also saw Ryan Crouser from the United States win a third consecutive men's Olympic shot put gold.
And on the clay courts of Roland Garros, Zheng Qinwen became the first Chinese player to win Olympic tennis singles gold as she defeated Croatia's Donna Vekic 6-2, 6-3 in the final.
A total of 29 golds were up for grabs on Saturday, with France, Australia, Britain and the United States chasing current medal table leader China.
