Lydia Jacoby golden, Naomi Osaka falls

Day four at the Tokyo Olympics will be headlined by one of the most anticipated events of 2021 — the women’s gymnastics team final.

However, an upset win for Alaskan teen Lydia Jacoby in the women's 100-meter breaststroke provided an early highlight in Tuesday's action. Jacoby edged U.S. teammate Lilly King, the defending champion in the event from the 2016 Games in Rio. King ended up getting bronze, one of three on the day for American swimmers.

Another upset occurred at the Ariake Tennis Park Centre Court as No. 2 seed and Olympic cauldron lighter Naomi Osaka lost in straight sets to Marketa Vondrousova 6-1, 6-4. Osaka had dominated in the first two round of the Games, but racked up 32 unforced errors in her loss on Tuesday.

After a not-so impressive qualifying round, the Simone Biles-led U.S. women’s gymnastics team will look to reclaim its status as heavy favorites and win a third consecutive team gold medal early Tuesday in the U.S. (6:45 a.m. ET).

Team USA can also secure another gold medal in softball after a walk-off win against Japan on Monday — the same team they will face in the gold medal game at 7 a.m. ET. U.S. softball will also look to avenge a gold-medal loss in the 2008 Olympics to Japan, the last time the sport was part of the Summer Games.

Meanwhile, the outdoor events could all face weather implications as tropical storm Nepartak is expected to hit Japan on Tuesday.

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TOKYO – Two things seemed clear through the first two days of Naomi Osaka’s quest to win an Olympic gold medal. The first was how much it meant to her to be representing Japan, which bestowed her the honor of lighting the Olympic flame at the Opening Ceremony. The second was that her tennis seemed up to the occasion.

But that’s the amazing thing about sports. Everything we think we know can change in the blink of an eye.

Just like that, Osaka’s run is over after a shocking 6-1, 6-4 loss to Marketa Vondrousova of the Czech Republic, continuing the trend of high seeds bowing out early in the women’s singles draw.

Based on nearly every factor imaginable, it would have been hard to see this coming. Vondrousova, a 22-year old lefty, surprisingly made the French Open final in 2019 but has just one WTA title to her name. Her form lately has been inconsistent at best, having fallen to No. 42 after a stint in the top 20.

This was Osaka’s first tournament since withdrawing from the French Open, citing the need to take a break for her mental health. Her focus now will turn to defending her U.S. Open title later this summer, but in many ways, her entire year had been built around trying to win a gold medal in Tokyo.

Now that dream is gone, opening up the field reminiscent of the 2016 Olympics when longshot Monica Puig took gold.

-- Dan Wolken

American surfer Carissa Moore will compete for an Olympic gold medal Tuesday after winning her semifinals heat.

Moore, a four-time world champion, defeated Amuro Tsuzuki of Japan by a thin margin.

She will face South Africa’s Bianca Buitendag, who defeated American Caroline Marks in the other semifinals heat.

The top-ranked women’s surfer in the world, Moore, 28, entered the competition as the favorite.

Earlier in the day, she won her quarterfinals heat against Silvana Lima of Brazil.

American surfer Caroline Marks will compete for an Olympic bronze medal Tuesday after coming up short in her semifinals heat.

Marks, 19, lost to Bianca Buitendag of South Africa at Tsurigasaki Surfing Beach.

Marks, a native of Florida, will face the loser of the semifinals heat between fellow American Carissa Moore, a four-time world champion, and Amuro Tsuzuki of Japan.

Earlier in the day, Marks won her quarterfinals heat against Brisa Hennessy of Costa Rica.

-- Josh Peter

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TOKYO – Alaskan teen Lydia Jacoby pulled off the upset in the women’s 100-meter breaststroke, becoming the first American woman to win gold in swimming in these Olympics.

She beat U.S. teammate Lilly King, who was chasing her second consecutive Olympic gold medal in the breast.

Jacoby won in 1:04.95 followed by Tatjana Schoenmaker from South Africa and King, who took bronze.

King, 24, brashly predicted at last month’s U.S. Olympic trials that American women could win every individual race at these Olympics.

She also famously called out Russia’s twice-suspended Yulia Efimova, slapping the water in celebration after defeating her in Rio in 2016.

-- Christine Brennan

The U.S. men's rugby team fell to South Africa 17-12 to finish second in Pool C after posting a 2-1 record in round-robin play.

The U.S. will play Great Britain in the quarterfinals Tuesday at 5 a.m. ET. Great Britain won silver in the 2016 Olympics, which marked the return of rugby sevens to the Olympic docket after 92 years.

The other quarterfinal matches are New Zealand-Canada (4:30 a.m. ET), South Africa-Argentina (5:30 a.m. ET) and Fiji-Australia (6 a.m. ET).

Fiji are the reigning gold medal winners. The U.S. did not qualify for the quarterfinals in 2016.

-- Jim Reineking

TOKYO — Ryan Murphy fell short of his goal of repeating as Olympic champion in the men's 100 meter backstroke as Russian Olympic Committee swimmers Evgeny Rylov (51.98 seconds) and Kliment Koleskinov (52.00) took gold and silver ahead of him on Tuesday.

Murphy swam a 52.19 to claim bronze, despite entering the final with the top time of 52.24, five one-hundredths of a second ahead of Koleskinov.

The University of California-Berkeley graduate also won gold in the 200-meter back and the 4x100 medley relay in Rio, his first Olympics. He can still repeat in the 200-meter backstroke as qualifying heats begin on Wednesday.

-- Chris Bumbaca

TOKYO – American Regan Smith, the former world-record holder in the women’s 100 backstroke, won the bronze medal Tuesday morning at the Tokyo Aquatics Centre

Current world-record holder Kaylee McKeown of Australia won gold in 57.47 seconds followed by Canadian Kylie Masse in 57.72. McKeown's time was an Olympic record.

Smith was third in 58.05.

Smith, 19, one of 11 teenagers on the U.S. Olympic swimming team, the most since 1996, set the Olympic record in qualifying Monday in 57.86 seconds. She was the third swimmer to do it here, following Masse and McKeown. They are the only three swimmers in history to break 58 seconds.

-- Christine Brennan

TOKYO – The second-seeded U.S. women’s beach volleyball duo of April Ross and Alix Klineman remain undefeated (2-0) in pool play at the Tokyo Olympics.