TOKYO — Britain won the mixed medley relay in a time of 3:37:58, setting a world record in the first time the event was held at the Olympics. China took silver and Australia bronze, followed by Italy and the United States.

The mixed medley was the last final of the session, and one of the wackiest and most strategic of the meet.

Teams swim 100 meters of each stroke, back, breast, butterfly and free. Each team featured two men and two women, but each country decided the order in which they swam.

The American team of Regan Smith, Andrew Wilson, Tom Shields and Abby Weitzeil had the second-fastest qualifying time, well behind that of Britain, which established an Olympic record of 3:38.75.

For the final, however, the U.S. fielded Ryan Murphy (backstroke), Lydia Jacoby (breaststroke), Torri Huske (butterfly) and Caeleb Dressel (freestyle).