Budapest (AFP) - Australian 18-year-old Mollie O'Callaghan overcame "panic" to edge world record holder Sarah Sjostrom and become the youngest women's 100m freestyle world champion in more than 30 years on Thursday.
Lilly King added to her collection of gold medals when she won the women's 200m breaststroke while another American veteran Ryan Murphy won the men's 200m backstroke.
Australian Zac Stubblety-Cook took the men's 200m breaststroke.
The American men finished the evening by winning the mens 200m relay.
O'Callaghan, a double Olympic relay gold medallist, edged the 28-year-old Sjostrom of Sweden by 0.13sec.American Torri Huske took bronze.
At 18 years and 82 days, she became the youngest winner of the 100m freestyle since 1991, when Nicole Haislett of the United States won the title at 18 years and 22 days.
O'Callaghan said she had suffered badly from pre-race nerves.
"It was bad, the worst ever," she said.
"I was panicking in my bed, having a little bit of a cramp in my leg, just feeling dizzy, feeling out of it, starting to panic, but I knew I had my teammates there...I guess that kind of uplifted me for the race."
It was Sjostrom's 16th World Championship medal but while she has eight golds, she has never won the 100m free.This was her fourth silver.
She also has world-championship and Olympic bronzes in the race.
'Complete the set'
King had dominated the 50m and 100m breaststroke at the last two world championships and also won gold in the 2016 Olympics in the 100m breaststroke.
After she missed a medal in the 100m breast on Tuesday, her college coach, Ray Looze, told American media that she was racing at "80 percent".
On Thursday, she came from fifth to grab victory in 2min 22.41sec.Australian Jenna Strauch was second at 0.63 with American Kate Douglass third.
"It's really nice to be able to complete the set, I guess I'm a distance swimmer now," said King after her first gold at the longest breaststroke distance.
King said the setback earlier in the competition had motivated her.
"Anytime I have a bad swim I feel like I have a lot of haters out there, so just to prove them wrong is good," she said
Murphy ended a long streak of duller coloured medals when he won the men's 200m backstroke.
Since grabbing two individual Olympic golds in Rio in 2016, the American had collected six silvers and two bronzes in Olympics and worlds, including a silver in the 100m backstroke in Budapest.
The 26-year-old won in 1:54.52, 0.64sec ahead of Briton Luke Greenbank with another American, Shaine Casas third.
"That ws a far from perfect race but I managed it," Murphy said.
Australian Stubblety-Cook, the Olympic champion, came from last after the first lap to win the men's 200m breaststroke.
Dutchman Caspar Corbeau started off at world record pace, but faded and Stubblety-Cook, Yu Hanaguruma and Erik Persson, who had conserved energy at the back, came through.
The Australian won in 2:07.07, 1.31sec ahead of the Japanese and the Swede who tied for the silver.
Kristof Milak, the Hungarian who said after winning the 200m butterfly that the Duna "is my pool", strolled out for butterfly 100m semis like a lord strolling his estate.
Milak has struggled to catch American Olympic and world champion Caeleb Dressel in the 100m butterfly.
With the American heading home, the Hungarian star justified his aura of confidence by comfortably swimming the fastest time.
He finished in 50.14sec, 0.67sec quicker than Naoki Mizunuma of Japan.
In the 50m, another event that Dressel has dominated in recent seasons, Briton Benjamin Proud was fastest in the semis.
