Ariarne Titmus turned swimming's race of the century into a glorious golden personal procession.
Australia's women's 4x100m freestyle relayers stretched the nation's dominance in the event to a remarkable fourth Olympics.
Elijah Winnington's previously bitter Olympic experience now has a silver lining.
And Australia's male 4x100m freestyle relayers captured a coveted silver medal on a stunningly successful opening night for the nation at the Paris pool.
The Dolphins harvested two gold and two silver medals from Saturday night's four finals, adding to cyclist Grace Brown's earlier time trial triumph, a mighty day one haul that puts Australia on top of the medal table in Paris.
Titmus was in disbelief at becoming just the second Australian woman swimmer to keep an Olympic crown.
The legendary Dawn Fraser, who watched from the raucous grandstands at the Paris La Defense Arena, won 100m freestyle gold at the 1956, 1960 and 1964 Games.
"I can't really believe that's me," Titmus said of joining Fraser.
In her hyped final, the Tasmanian blitzed her rivals, American legend Katie Ledecky, who finished third, and Canadian teen Summer McIntosh, who placed second.
"It's fun racing the best in the world. It gets the best out of me," Titmus said.
"I hope with all the hype we have lived up to expectations."
The 23-year-old led from go to whoa to claim the third Olympic gold medal of her career, after her 200m-400m freestyle double at the Tokyo Games three years ago.
"I just look at myself and I'm so normal ... I'm just the same old goofy Tassie girl living out her dream," she said after clocking three minutes 57.49 seconds to win comfortably from McIntosh (3:58.37) and Ledecky (4:00.86).
The victory of Australian swimming's unbeatables, the women's freestyle relayers, is the country's fourth-straight Olympic gold in the event.
Emma McKeon added a sixth gold to her glittering career collection, an Australian record - she entered Paris with five, the same as Ian Thorpe.
"I can't believe where I'm at right now," she said.
Shayna Jack's recovery from a two-year doping ban which cost her any chance of racing at the Tokyo Games of 2021, is now complete.
"Making the Olympic team was my first step and that was one of the most exciting moments," Jack said.
"I didn't know where that was going to take me. This is definitely a great start."
In the final, McKeon, Jack, Mollie O'Callaghan and Meg Harris set an Olympic record of 3:28.92 to win by a whopping 1.28 seconds from the United States.
In the men's equivalent, Kyle Chalmers enhanced his status as Australia's greatest male relayer with a trademark late surge.
Chalmers dived in with Australia fourth but steamed to silver - his 100m split of 46.59 seconds was the fastest of the race.
"I love being part of the relay .... I love swimming for the team, that's my pride and joy and that's why I swim," he said.
Chalmers' teammate Elijah Winnington thanked God for his silver medal in the men's 400m freestyle.
Three years ago at the Tokyo Games, Winnington entered as hot favourite but cold-crashed to seventh.
He has a silver medal after a heat swim in the Tokyo Games from the 4x200m relay, but said he couldn't bear the sight of it.
"I haven't ever told anybody this, but I've never actually looked at that medal because I didn't think I'd earned it," he said.
Winnington said winning silver in Paris was "unbelievable".
"For a couple of months there, I didn't think I was going to swim again," he said of his crushing post-Tokyo disappointment.
Winnington's compatriot in Paris and pre-race fancy Sam Short finished fourth.
