Caeleb Dressel and the U.S. 4x100m freestyle relay broke a nine-year-old world record to open the world short-course swimming championships in Hangzhou, China, on Tuesday.
Dressel, the seven-time 2017 World champion, led off a quartet that included fellow Rio 4x100m free gold medalists Ryan Held and Blake Pieroni, plus Michael Chadwick. Dressel opened a .56 lead that the Americans never relinquished, holding off Russia by .08.
The U.S. also won the women’s 4x100m free, anchored by Kelsi Dahlia, who earned four relay golds at the 2017 Worlds. Mallory Comerford overtook the Netherlands on the third leg, with Dahlia holding off triple Olympic champion Ranomi Kromowidjojo by .24.
Short course worlds are held in even-numbered years in a 25-meter pool rather than the 50-meter pool used at the Olympics. U.S. Olympic champions Katie Ledecky, Simone Manuel and Lilly King are among those not competing this week.
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In other events Tuesday, Hungarian Katinka Hosszu extended her all-stroke dominance, winning the 400m individual medley by 4.44 seconds over American Melanie Margalis. Hosszu swept the IMs at the Rio Olympics, the last three long-course world championships and the 2016 short-course worlds.
Daiya Seto, in line to be one of the host nation’s stars at the Tokyo Olympics, broke Chad le Clos‘ world record in the 200m butterfly and edged the South African by .08 for gold.
The U.S. also earned individual silvers in the 200m free (Comerford) and 200m IM (Josh Prenot).
Worlds continue Wednesday, live on Olympic Channel: Home of Team USA and streaming on NBCSports.com/live and the NBC Sports app.
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