The two-time world champion touched in 49.45 seconds to better his own world best 49.50 set at the 2019 world championships.
Hungarian 200m fly champion Kristof Milak was second in 49.68 and Noe Ponti of Switzerland third in 50.74.
- Australia's McKeown wins women's Olympic 200m backstroke gold
Australian swimming sensation Kaylee McKeown completed the Olympic backstroke double Saturday, adding the 200m title to her 100m crown.
The 20-year-old swam a blistering final 50m to touch in 2min 04.68sec ahead of Canada's Kylie Masse (2:05.42) and fellow Australian Emily Seebohm (2:06.17).
- American Ledecky wins third straight Olympic 800m freestyle title
American star Katie Ledecky stormed to her third straight Olympic 800m freestyle title Saturday with a dominant swim to bank her fourth Tokyo medal.
Ledecky touched in 8mins 12.57 to outpace Australian arch-rival Ariarne Titmus, who clocked a personal best 8:13.83 to take silver ahead of Italy's Simona Quadarella (8:18.35).
- Britain smash world record to win inaugural Olympic mixed 4x100m relay gold
Adam Peaty's British team smashed the world record to win the inaugural Olympic 4x100m mixed medley relay gold medal on Saturday, outgunning China and Australia.
Their four-strong team of Kathleen Dawson, Peaty, James Guy and Anna Hopkin touched in 3min 37.58sec to break the previous 3:38.41 mark set by China in Qingdao last year.
The Chinese were second in 3:38.86 with Australia third in 3:38.95. The Caeleb Dressel-led United States came fifth.