Lydia Jacoby of the U.S. upsets Lilly King in the 100-meter breaststroke.

TOKYO — As expected, an American woman was edging ahead in the women’s 100-meter breaststroke on Tuesday morning.

But the American was not named Lilly King, the defending Olympic champion and world-record holder. Instead, in the race of her life, Lydia Jacoby, a 17-year-old Alaskan, tapped the wall first and then gazed toward the scoreboard at the Tokyo Aquatics Center. It took her a nanosecond to register the result.

“Insane,” she said.

Swimming has delivered surprises at the Tokyo Games, and Jacoby’s gold medal performance ranked among the most shocking so far. The first Alaskan to compete in Olympic swimming, she trains with her local club, the Seward Tsunami Swim Club, which is not to be confused with the usual powerhouse programs from California and Texas.

On Tuesday, against the very best in the world, Jacoby proved that geography did not seem to matter that much at all.

“I think that me coming from a small club and a state with such a small population just shows everyone that you can do it no matter where you’re from,” said Jacoby, who will be a senior in high school this fall.

Classmates and friends cheered her on from afar at watch parties in Seward — and went bonkers when she chased down Tatjana Schoenmaker of South Africa in the closing meters. (The videos went viral within minutes.)

King, 24, claimed the bronze — an anticlimactic result for one of the sport’s most outspoken personalities. Despite having aimed to become the first woman to win two gold medals in the event, she said she was pleased with her race.

“And so excited for Lydia,” said King, who had not lost a race in the 100-meter breaststroke since 2015. “I love to see the future of American breaststroke coming up like this and to have somebody to go at it head-to-head when we’re in the country.”

Another relative upset played out in the men’s 100-meter backstroke, an event that Americans had won at every Olympics since 1996. But Ryan Murphy, the defending Olympic champion, got off to a slow start and finished third behind a pair of Russians, Evgeny Rylov and Kliment Kolesnikov.

Murphy said he was not disappointed.

“That was my best swim of the year, so it’s nice to be able to do that in the pressure-packed final,” he said, adding: “Shoot for the stars, land on the moon. That’s kind of what it is. Winning an Olympic gold means you’re the best in the world. Being third in the world is no slouch.”

King had made waves at the 2016 Olympics in Rio de Janeiro for engaging in a personal rivalry with Yuliya Efimova of Russia, a six-time world champion. Ahead of Rio, Efimova had served a 16-month suspension for doping, then was allowed to compete despite failing another drug test.

King was highly critical of that decision. After outswimming Efimova in the Olympic final, King splashed water in Efimova’s lane. (King later said it was unintentional.)

Yet in the run-up to the Tokyo Games, King continued to be outspoken about cheating, expressing concern about spotty drug-testing protocols during the pandemic.

On Tuesday, there was no apparent controversy — only good vibes. King was finishing up her interviews in the media area when Jacoby arrived.

“Off to you, kiddo,” King told her. “No international incidents today.”