Shanghai, China: Japan's Daiya Seto smashed Chad le Clos's short-course record in the men's 200m butterfly as he grabbed gold at the world championships to stun the South African on Tuesday.
The 24-year-old Seto pipped his more famous rival by only 0.08sec to make a piece of history on the first day of action in the Chinese city of Hangzhou.
Seto, who won bronze in the 400m medley at the Rio 2016 Olympics, recovered from a comparatively slow start to hold off Le Clos down the stretch and triumph in 1min 48.24sec.
It was a disappointing silver for the 26-year-old Le Clos, the reigning long-course and short-course world champion.
He had also held the short-course record of 1:48.56, set in Singapore in 2013, until Seto bettered it in style.
A distant third was China's Li Zhuhao.
"I didn't expect the world record," Seto was quoted by the Xinhua news agency as saying.
"Now I will focus on the 400m IM (individual medley) and I hope I can break the 400m IM world record also."
Australian teenager Ariarne Titmus stormed back to win the women's 200m freestyle gold and underline her status as a rising star of swimming.
The 18-year-old, who won 400m and 800m freestyle gold at the Commonwealth Games in her home country earlier this year, ran down the American Mallory Comerford to seal victory in a thrilling race.
Titmus was back in third after 150m, but she burst to the finish in a time of 1:51.38 to relegate Comerford into silver, with Femke Heemskerk of the Netherlands taking bronze having led for half of a nail-biting race.
Titmus put her head in her hands when she realised she had taken gold, powering to the win with 0.43sec to spare over Comerford.
Hungary's Katinka Hosszu, a triple gold medallist at the 2016 Rio Olympics, was a strong favourite in the women's 400m individual medley -- and she did not disappoint.
Dubbed the "Iron Lady", Hosszu dominated the short course world championships two years ago in Canada, carrying home seven golds.
She wasted no time getting her first victory in Hangzhou, sealing a dominant win in 4:21.40, comfortably ahead of Melanie Margalis of the United States, who won silver, more than four seconds back.
Third was France's Fantine Lesaffre.
Hosts China clinched their first gold medal of the meeting when Wang Shun took victory in the men's 200m individual medley.