For the first time ever in Olympic competition, men and women raced side-by-side in the pool Thursday in the preliminary heats of the mixed 4x100m medley relay.
The mixed medley relay pits teams of four swimmers — two male and two female — against each other with each team member swimming one of the four strokes. There is no rule dictating which strokes must be swam by men and which must be swam by women.
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Since the event debuted in world championship competition in 2015, it has often had the feel of an "all-star" race as nations' top male and female swimmers team up. In the final at 2019 Worlds, for example, the United States fielded a star-studded team of Olympic gold medalists Ryan Murphy (backstroke), Lilly King (breaststroke), Caeleb Dressel (butterfly) and Simone Manuel (freestyle).
SEE MORE: 2019 Worlds: Australia beats USA for mixed medley relay gold
In the prelims in Tokyo, the U.S. opted for a less experienced quartet to lock up a spot in the final. Regan Smith led off in backstroke, followed by Andrew Wilson in breaststroke, Tom Shields in butterfly and Abbey Weitzeil in freestyle, as the U.S. team finished in 3:41.02. It is expected that at least one — and potentially as many as all four — of the prelim swimmers will be replaced for Saturday's final. Dressel is likely to race as part of his chase for six Tokyo gold medals.
The U.S. advanced second behind only Great Britain, who tabbed something much closer to an "A-team" including men's 100m breaststroke world record holder Adam Peaty.
China won the second semifinal in 3:42.29, qualifying third.