Katie Ledecky has given the United States its first swimming gold medal of the Rio Olympics with a world record in the women’s 400-meter freestyle.

The result was totally expected. Ledecky has dominated the longer freestyle events since winning gold in the 800 free at the London Olympics as a 15-year-old. She was doing nothing but racing against the clock Sunday night. No problem there.

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Ledecky kicked off the first wall with a lead of nearly a body length and steadily pulled away from the overmatched field — as well as the world-record line superimposed on the video screen as her powerful arms churned through the water.

When Ledecky saw the time — 3 minutes, 56.46 seconds — she let out an uncharacteristic scream and pumped her right fist. The 19-year-old crushed the mark of 3:58.37 that she set nearly two years ago on the Gold Coast of Australia, and had been chasing ever since.