Swimming-American Dressel sets world record in men's 100m butterfly at worlds

American Caeleb Dressel set a world record of 49.50 seconds in the semi-finals of the men's 100 meters butterfly at the world championships in Gwangju on Friday.

Dressel shaved 0.32 seconds off Michael Phelps' former record of 49.82 set at the 2009 worlds in Rome.

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