Bethesda’s Katie Ledecky wins gold in the 200-meter freestyle during the Olympic Games on Tuesday night in Rio De Janeiro. (Jonathan Newton/The Washington Post)

It’s not as if the idea of Katie Ledecky losing at swimming was completely implausible. She finished second in a semifinal as recently as Monday. At various meets at various times, she has been known to enter events — an individual medley in Atlanta, a butterfly in Mesa — where she stands no chance, just for kicks, just for variety’s sake, just to post a time.

But on a stage such as this, the 2016 Rio de Janeiro Olympics, in a race such as the one in which she would be swimming Tuesday night, the final of the women’s 200-meter freestyle, Ledecky simply does not lose. Not even when the swimmer next to her was faster this year, and this week. Not even when she revs her engine so hard, she nearly throws up on the last lap.

For the 14th time in her career, Ledecky faced a final in a major international race, and for the 14th time, she won. Few, if any, had taxed her so much. But that only made her narrow victory that much sweeter. Pushing herself beyond her normal, self-regulated limits, Ledecky held off world No. 1 Sarah Sjostrom of Sweden over the final lap to finish in 1:53.73 and win the gold medal by 35 hundredths of a second. Australia’s Emma McKeon won bronze in 1:54.92.

“That was such a tough race,” Ledecky said. “Everything was hurting, and I knew I wouldn’t be able to see most of field on last 50, so I knew I had to just dig deep. When I saw it [first place] on scoreboard, it sunk in then. I was done when I touched the wall. I gave it everything I had there, and I knew I had to. It was such an incredible field, and I was just honored to be a part of that.”

After Katie Ledecky recently broke her own world record in the 2016 Rio Olympics, check out her interview with Brandon Parker from the 2015 Winter All-Met photo shoot. (TWP)

The victory gave Ledecky, a 19-year-old from Bethesda, her third medal, and second gold, of the Rio Games, to go along with the single gold she won in London four years ago.

When it was over, rather than slap the water in exultation as she had after winning the 400 free two nights earlier, all Ledecky could muster was a weak grin and a massive exhale, whatever was gurgling up from below thankfully pushed back down.

“It went away,” she said of the feeling of almost vomiting. “Everything hurt at the end. It means I pushed myself to the max.”

Ledecky, in Lane 5, made the first turn in fifth place, with McKeon, in Lane 7, holding a slight lead. By the halfway point, she had climbed to second, just six-hundredths of a second behind McKeon. But then here came Sjostrom from Lane 4. Ledecky knew she had made a poor second turn — starting her flip too soon — and made a decision to push herself in the third 50 to give herself the lead entering the final lap.

The strategy worked — she turned at the 150 mark with a lead of .40 seconds over Sjostrom — but there was a cost: Halfway through the final lap, she felt a familiar “burp” rising up, the kind she experiences when she has pushed herself to the brink, and that sometimes leads to actual vomit.

“I could feel it was coming,” she said, “and I just needed to get my hand to the wall.”

Ledecky had led the world rankings in the 200 free for most of the year, following a 1:54.43 in Austin in January, but the lead was understood to be tenuous. Sure enough, at an Olympic-tuneup meet in her native country in July, Sjostrom, 22, threw down a 1:54.34, taking over the top ranking from Ledecky and putting the two champions on a collision course in Rio de Janeiro.

Katie Ledecky developed the "gallop" in her stroke with former coach Yuri Suguiyama. It gives her an advantage in the pool over her female competitors since most do not have the strength to sustain it. (Jayne Orenstein/The Washington Post)

The stakes were raised further Sunday night, when both swimmers set world records in other events: Sjostrom in the 100 butterfly, Ledecky in the 400 free. If Ledecky was clearly dialed-in, so, too, was Sjostrom. In a head-to-head matchup in a 200 free semifinal Monday night, Sjostrom out-touched Ledecky by sixteen-hundredths of a second, ensuring the two would be in adjacent lanes in the middle of the pool for Tuesday night’s final.

“I’d never bet against her,” Ledecky’s coach, Bruce Gemmell, said.

Every shred of evidence in the days leading up to Tuesday night’s 200 – her consistently superb training, her two sizzling swims here as the anchor for the silver-medal-winning 4x100 free relay team, her world-record-shattering performance in the 400 free — pointed to the conclusion that Ledecky was simply in the best form of her life. Her monster showing Tuesday night only proved it definitively.

If she wins nothing else in Rio, Ledecky will leave as one of just four American women with three individual Olympic gold medals, joining Janet Evans (1988, 1992), who won four, and Debbie Meyer (1968) and Brooke Bennett (1996, 2000), who won three each.

But of course, Ledecky could — and should — leave Rio with two more golds before these Olympics are over.

She will anchor the women’s 4x200 free relay Wednesday night, a race in which the United States has won gold in four of the past five Olympic games, as well as the 2015 world championships. She will then close out her Olympic meet with the 800 free, with heats Thursday afternoon and final Friday night, an event in which no one in the world has been within 11 seconds of her this year and no one in history has been within seven.

The 200 has never been Ledecky’s best race. In 2012, the same year she won the 800 free in London as a 15-year-old, she ranked just 54th worldwide in the 200. But by 2013 she was ranked ninth, by 2014 she was winning it at the Pan Pacific Championships and by 2015 she was the world champion. Still, unlike the 400 and 800, it has never been a race she could win simply by showing up.

“The 200 free is such a more stressful event for me than the 400 or 800,” she said, “just because I can’t really settle into my rhythm. It’s one mistake and you’re done.”

Halfway through the Olympic meet, Ledecky is closing in on history: She is on the verge of becoming the first swimmer since Meyer in 1968 to sweep the 200, 400 and 800 freestyles, and the third American woman, after Amy Van Dyken in 1996 and Missy Franklin in 2012, to win four golds in a single Olympics.

“Usually I don’t really think about the history like that, but I think I’m just really honored to be part of the tradition of American freestyle swimming,” Ledecky said. “Debbie told me she wanted me to [match her], and I don’t want to let her down.”