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GWANGJU, South Korea — There could be no sulking after Katie Ledecky was defeated in the 400-meter freestyle Sunday at the FINA world championships. She was due back in the pool just 15 hours later for a 1,500-meter qualifying heat.

If losing a signature race was unfamiliar, rebounding from disappointment was completely new territory. But with four more races on tap at the year’s biggest meet, Ledecky knew she had no choice.

So, she was back in the pool Monday, doing what she does best, almost mechanically windmilling her arms and gliding across the water. Forty strokes in one direction. Forty strokes back.

“If anyone is equipped to deal with this, it’s Katie Ledecky,” said Yuri Suguiyama, her youth coach at Nation’s Capital Swim Club.

The next several days will force Ledecky to do something she has rarely had to think about: shake off disappointment, channel her emotions, quickly turn the page. After Ariarne Titmus, the 18-year old Australian, chased down Ledecky in the final lap of Sunday’s 400 — one of Ledecky’s three dominant distances — the Washington, D.C., native returned to the athletes’ village and had a full night to refocus.

She returned to the Nambu University Municipal Aquatics Center on Monday morning for the 1,500-meter heats. She posted the fastest time — 15:48.90, which is a great mark for any other swimmer. It was the year’s fourth-fastest time, in fact, but gave few hints as to how Ledecky might perform in Tuesday’s 1,500 final. At the world championships four years ago, Ledecky broke the world record in the qualifying heats with a time of 15:27.71. The next day she broke it again in 15:25.48. (And last year lowered it again — to 15:20.48.)

She looked tired following Monday’s heat and didn’t talk to reporters afterward, uncharacteristic for her. “I need to get my fight back,” she said the night before.

No swimmer, of course, is invincible. Not forever at least. Michael Phelps might have been unbeatable in 2007 and ’08, but he also retired with seven individual silver medals and a bronze from his 11 trips to the Olympics and world championships.

“You look back at Michael’s career,” said Greg Meehan, Ledecky’s coach, “some ups and downs, some wins and losses, always learning from each experience.”

Ledecky’s experiences have been overwhelmingly positive. At 22, she has made domination look routine. She has faced no serious injury, has been dealt no major setback. Most elite swimmers — virtually every other Olympic champion — is somewhat accustomed to losing a big race on a big stage at some point, dusting off the disappointment and pulling themselves back up.

Ledecky has been in a league of her own, though. In major international competitions — the Pan Pacific championship, world championships or Olympics — she’d competed in 23 individual races entering this week. She’d finished in first place 21 times, her only losses coming at 200 meters each of the past two years.

Her best distances, the ones at which she holds world records, have always been the 400, 800 and 1,500, and Sunday was the first time she lost one of these races at a big meet.

As much as Ledecky trains — her work ethic around the pool has always been lauded by coaches — there’s no practice for losing, for feeling pain, for regrouping. You just have to do it.

And Ledecky actually has — just not much and not in a long while. While she has made a comfortable home atop the medals podium, she also remembers the early losses that helped get her there. Until Sunday, perhaps none stung as much as the 2012 U.S. Olympic trials, the very meet that launched her into this otherworldly strata of elite swimmers.

Ledecky was all of 15 years old then and had just wrapped her freshman year at Stone Ridge School of the Sacred Heart in Bethesda, Md. She had three big races at the trials in Omaha The first one — the 400 free — was considered her best shot at making the U.S. Olympic team bound for London.

On the second day of trials, she broke a 24-year-old national record for her age group that was held by Janet Evans. But her time — 4:05.79 — was only good enough for third place. Only the top two finishers make the team.

“In most cases, that would have devastated most 15 year-old swimmers,” said Suguiyama, now the head women’s coach at Wisconsin, “but after the initial shock and disappointment, we focused on the positive — something I’m sure Greg Meehan will be doing — and Katie recovered.”

The next day in the 200 free, she finished in ninth in the semifinals and missed making the finals by 0.02 seconds. That left her with just one final shot, and she had three days to calm her nerves.

A teenage Ledecky won the 800 in Omaha and punched her ticket to those London Games, where she became the youngest member of the U.S. team and would go on to win the first of her five Olympic titles.

“The rest,” said Bruce Gemmell, who later coached Ledecky at Nation’s Capital Swim Club, “is history.”

There was no way of knowing at the time that Ledecky was embarking on a stretch of nearly unmatched dominance. She has consistently shown what it is like to win big, and it wasn’t until Sunday night in Gwangju that she really had to deal with a big loss.

“While I’m sure this one will sting, I think she’ll be able to get over it because she has such a strong sense of self, a comfort and confidence in her own skin,” Suguiyama said, “as well as an unbelievable support system in her family and the U.S. national team.”

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