Adam Peaty's British team smashed the world record to win the inaugural Olympic 4x100m mixed medley relay gold on Saturday, outgunning China and Australia.
Britain's 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 and Australia third in 3:38.95. The Caeleb Dressel-led United States were relegated to fifth.
The mixed relay was one of three swimming events debuting in Japan along with the men's 800m freestyle and women's 1500m freestyle.
Teams comprising two women and two men, with each of the four swimmers allocated to one of the four traditional medley strokes -- backstroke, breaststroke, butterfly and freestyle.
Britain chose to lead off with Dawson, up against American backstroke giant Ryan Murphy and Australia's Kaylee McKeown, who won the 200m individual title minutes earlier.
Peaty, who won 100m breaststroke gold in Tokyo, then took up the baton.
Guy swam a storming butterfly leg to hand over to Hopkin, who brought it home ahead of China's Yang Junxuan, Australian 100m freestyle champion Emma McKeon and a chasing Dressel.