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Round One of Ariarne Titmus versus Katie Ledecky goes to Ariarne Titmus.

Titmus took home gold in the 400-meter freestyle with a time of 3:56.69, setting an Australian record and falling just short of Ledecky’s world record from the 2016 Olympics. Ledecky came in second at 3:57.36, her fastest time since setting the world record in Rio.

The swimmers’ times were the second and third fastest in history. Titmus became the first swimmer to defeat Ledecky in an individual Olympic event.

The win spurred an immediately iconic reaction by Titmus’ coach Dean Boxall, who began coaching Titmus five years ago. Back then, Titmus was 16 seconds off of Ledecky’s world-record time.

Ledecky and Titmus return to action in the semifinals of the 200m freestyle on Monday at 9:30 p.m. ET on NBC. Ledecky, whose Olympic performance in 2016 (four golds, one silver) was the most decorated by a U.S. female athlete, won her heat of the 200m qualifiers Sunday night with a time of 1:55.28.