South Africa's Roland Schoeman smashed his own world record to win the 50m butterfly gold at the World Swimming Championships in Montreal on Monday.
The 25-year-old clocked 22.96 seconds to shave 0.05 off the global mark of 23.01 he set in Sunday's semi-finals.
Former world record holder Ian Crocker was second for the US in 23.12 and Sergiy Breus of Ukraine third in 23.38.
America's Jessica Hardy, 18, also set a world record when she won the women's 100m breastroke semi-finals in 1:06.20.
Hardy was competing in her first international meet but her time was 0.17 faster than the previous best of 1:06.37 set by Australia's Leisel Jones at the 2003 worlds in Barcelona.
And while the teenager admitted her achievement had taken her by surprise, she revealed she believes she can go even quicker.
"It was definitely a shock, an awesome shock," she said. "But I feel like there's still room for improvement."
Schoeman was also stunned by his record-breaking swim.
"I always think it's hard coming into a final of an event - you've got Ian Crocker, a (former) world record-holder, a lot of seasoned campaigners. Swimming your best time in a final is unexpected," he said.
Meanwhile, Brendan Hansen and Katie Hoff ensured it was a golden night for America in the pool.
Hansen touched home in 59.37 - 0.07 outside the world record of 59.30 he set at last year's US Olympic trials - to win the men's 100m breastroke from his longtime rival Japan's Kosuke Kitajima, who clocked 59.53.
The 23-year-old finished runner-up to Kitajima at the 2003 world championships in Barcelona then again at last summer's Athens Olympics.
"This was a second chance for me and I didn't want to screw it up," Hansen said.
"What makes a great swimmer is someone who can come back from a great disappointment and go even faster."
Hoff triumphed in the women's 200m individual medley.
The 16-year-old completed the four-length multi-discipline race in 2:10.41, just 0.69 outside Wu Yanyan's 1997 world record of 2:09.72.
Zimbabwe's Olympic backstroke champion Kirsty Coventry was second in 2:11.13, while Australia's Lara Carroll was third in 2:13.32.
Jess Schipper led an Australian one-two in the women's 100m butterfly final.
Schipper took the gold in 57.23, making her the third fastest woman in history in the event.
Compatriot Libby Lenton finished second in 57.37 and Poland's Otylia Jedrzejczak was third in 58.57.
Elsewhere, America's Michael Phelps recovered from his shock failure in the 400m freestyle on the opening day to qualify fastest for Tuesday's men's 200m final.
Phelps' rival, Australian Grant Hackett, who won the 400m, qualified fourth fastest for the 200m final.