Rio Olympics Today:

Swimming Gets Underway

By SAM MANCHESTER and VICTOR MATHERUPDATED 

Horton Beats Sun in 400 FreePhoto

Kosuke Hagino enjoyed his 400 IM victory. CreditDoug Mills/The New York Times

Mack Horton of Australia defeated the defending champion, Sun Yang, in the men’s 400-meter freestyle.

The two rivals started slowly and were only 6th and 7th after 150 meters behind Britain’s James Guy, who raced to the lead in world record pace. But the favorites moved methodically up to the lead, blowing past the fading Guy. Horton always led Sun and won in 3:41.55. Gabriele Detti of Italy was third, and the American Conor Dwyer, who had the fastest qualifying time, was fourth.

Sun and Horton had developed a sharp rivalry this week. Sun splashed and taunted Horton in the practice pool, and Horton responded by calling Yang a “drug cheat.” Sun served a three-month doping suspension in 2014.

Big Race for Japan: Kosuke Hagino of Japan won the first swimming final of the meet, the 400-meter individual medley, holding off a late rush from the American Chase Kalisz. Daiya Seto of Japan was third.

Hagino, the 2012 bronze medalist, trailed his countryman Seto after the opening butterfly leg, but took over quickly in the backstroke leg and never trailed again. His final time was 4:06.05.

Kalisz, a University of Georgia student, passed Seto in the third leg, the breaststroke, and made a game run at Hagino but could not catch him.

Gold No. 1 to American Shooter Virginia ThrasherPhoto

Virginia Thrasher, center, after winning a gold medal. Du Li, left, took the silver, and Yi Siling, right, won the bronze. CreditChang W. Lee/The New York Times

The first gold medalist was a 19-year-old West Virginia University sophomore, Virginia Thrasher.

With two shots to go in the women’s air rifle event, Thrasher, who is known as Ginny, led by 0.7 points. She coolly squeezed off shots of 10.5 and 10.4 to take gold. Two Chinese shooters, Du Li and favored Yi Siling won silver and bronze. Another American, Sarah Scherer was eighth.

Thrasher has only been shooting for five years, after she asked her father to take her deer hunting. She was N.C.A.A. champion as a freshman and surprisingly qualified for the U.S. team at the Olympic Trials. “For me, it has been a whirlwind of a summer,” she said. She will also compete in the 50-meter rifle, three positions, next Saturday, then head back to W.V.U.

“I get home 20 hours before the first class,” she said. “So I’ll be in physics at 8:30 a.m.”

Vietnam’s First Gold Medal: In the afternoon shooting event, history was made when Vinh Xuan Hoang won the men’s air pistol. It was the first gold medal in any sport for Vietnam. “Making this gold medal is a life memory, never forget this,” Hoang said. “Because first time making a gold medal for Vietnam.”

There Will Be More MedalsPhoto

Australia’s Bronte (right) and Cate Campbell, lead a formidable 4x100 relay team in Rio. CreditMichael Sohn/Associated Press

Now that the opening ceremony is over, let’s talk about actual sports. There’s a lot of them today. The U.S. women’s soccer survived a tough early challenge from France to win by 1-0. The U.S. men’s basketball team, fresh from their stay on a luxury yacht, faced absolutely no challenge from China tonight in a 119-62 destruction.

Women’s rugby arrived at the Olympics for the first time, in the form of rugby sevens. The United States split its two games, losing to Fiji, but beating Colombia. The women’s volleyball and field hockey teams won.

World Records Are Starting to Fall

Adam Peaty of Britain, the only man to break 58 seconds in the 100-meter breaststroke, lowered his world record in the preliminaries at the Olympic Aquatics Center on Saturday. Swimming well ahead of the field in smooth water, Peaty clocked a 57.55 to lower his year-old record of 57.92. The final is Sunday.

Today’s Big Events

GOLDSILVERBRONZECycling Menʼs Road Race belgiumGreg van Avermaet denmarkJakob Fuglsang polandRafal Majka

Shooting Womenʼs 10m Air Rifle united statesVirginia Thrasher chinaDu Li chinaYi Siling

Women's Soccer United States vs. France United States beat France, 1 – 0

Fencing Womenʼs Épée hungaryEmese Szasz italyRossella Fiamingo chinaSun Yiwen

Men's Basketball China vs. United States United States beat China, 119 – 62

Swimming Menʼs 400m Individual Medley japanKosuke Hagino united statesChase Kalisz japanDaiya Seto

Swimming Menʼs 400m Freestyle 9:30 p.m.

Swimming Womenʼs 400m Individual Medley 9:49 p.m.

Swimming Womenʼs 4x100m Freestyle Relay 10:24 p.m.

All Times Eastern Daylight Time

How to Watch

On TV: NBC

Streaming: NBCOlympics.com (computer) or the NBC Sports app(phone or tablet)

Before Watching the Games, Watch This ...Photo

American Simone Biles is expected to win the women’s all-round in gymnastics this year.CreditDoug Mills/The New York Times

There are world-class athletes, and then there are the world’s bestathletes. What’s the thing that separates the two? That’s what we set out to discover when planning for these Summer Games. It didn’t take us long to focus on Simone Biles, a 4-foot-something, once-in-a-lifetime whirlwind who absolutely dominates the world of gymnastics. Watch this interactive to find out how she does it.