One star runner defended his gold medal and one lost hers in an action-packed Saturday at Rio's Olympic Stadium that saw a new fastest woman in the world crowned.
Defending 10,000-meter gold medalist Mo Farah, of Great Britain, ran to gold again, despite tripping and falling a third of the way into the race. Then Jamaica's Elaine Thompson defeated the reigning 100-meter dash winner, Shelly-Ann Fraser-Pryce.
The action also saw Belgian Nafissatou Thiam win the heptathlon on the strength of long and high jump victories, while the men's long jump gold went to an American, though it wasn't immediately clear which one won the gold.
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American Jeff Henderson had the longest jump with 8.38 meters, but his celebration was delayed as countryman Jarrion Lawson's final jump was reviewed. His hand trailed through the sand behind his jump, which had otherwise seemed long enough, leaving him just outside the medal places.
Great Britain's Greg Rutherford took silver and South Africa's Luvo Manyonga won bronze
The 10,000 kicked off with Farah the dominant athlete in the sport, and he survived being tripped up about 11 minutes into the race in Rio. He quickly got up and stayed with the pack. When he crossed the finish line in front of Paul Tanui of Kenya, he collapsed to the ground in joy.
Farah has not lost a major race since taking silver in the 10,000 at the 2011 worlds. Ethiopia's Tamirat Tola and Yigrem Demelash had hoped to renew their nation's ownership of the race, but they finished third and fourth, respectively.
Among the sprinters vying for the title of fastest woman in the world were six to watch: Thompson and Fraser-Pryce, Murielle Ahoure of the Ivory Coast, Dafne Schippers of the Netherlands and Americans English Gardner and Tori Bowie.
But Thompson pulled ahead of the field in the sprint, putting daylight between her, second-place finisher Bowie and Fraser-Pryce.
Thompson and Fraser-Pryce celebrated together, the compatriots hoisting the Jamaican flag for a victory lap.
The final of the heptathlon's seven events, the 800m, finished off the night's action. Thiam ran it in a personal best 2:16.54, slower than many competitors but enough to stave off London 2012's gold medalist, Jessica Ennis-Hill, who secured a silver medal. Canada's Brianne Theisen-Eaton won bronze after a disappointing first day of competition.
Medals were awarded in the men's discus late Saturday morning. Germany's Christoph Harting took gold, Piotr Malachowski of Poland won silver and Daniel Jasinski of Germany was awarded bronze.
Also Saturday, Usain Bolt turned the stadium into his stage again for his first race at the Rio Games. Bolt had an easy win in his 100-meter heat.
Backed up by the trademark showmanship, Bolt did not disappoint his crowd.
All of a sudden, the 60,000-capacity stadium was filled with noisy fans on a sunny Saturday, a stark contrast with the opening day.
The roar was immense as soon as the Jamaican turned up on the track. Bolt returned the favor, spreading his arms wide and then applauding the crowd for their welcome and shouts of "Bolt-Bolt-Bolt."
The crowd had been difficult to calm and silence ahead of the start of races so far, but when Bolt put his fingers to his lips for silence, all went quiet.
Bolt may have been slow out of the blocks, but once his tall majestic frame is in full flow, there is no stopping him — in the heats at least.
"It wasn't the best start, it felt kind of sluggish," Bolt said, adding that he never has been a morning person and preparations for his noon-time race felt unusual. "I'm not used to running this early in the morning in any championships.
"Hopefully tomorrow when I come out I'll be feeling much better."
From lane six, he had time to look left four times to check out his opposition and then coasted across the line. He showed no ill effect from a hamstring injury ahead of the games. "My right leg is good."
His time of 10.07 seconds trailed that of his longtime rival Justin Gatlin by .06 seconds, but Bolt was running into a headwind while the American had the wind on his side.
In his heat, Gatlin showed just as much poise — without the showmanship. He shot out of the blocks and only let up at the very end for the best time of all racers.
Gatlin, who won gold at the 2004 Olympics, has been caught using banned substances twice (the first was later ruled as taken for attention deficit disorder) but the second brought a four-year ban for excessive testosterone. He told AP that he's not paying attention to what people are saying about him, and is not concerned with those who think he doesn't belong here.
Others to go through to the 100-meter semifinals were Nickel Ashmeade and Yohan Blake of Jamaica and American Trayvon Brommell.
On Saturday morning, women also begun their heats in the 400m.
Allyson Felix, who won't get a chance to repeat for gold in the 200, won her heat in the 400m with 51.24 seconds. She won the U.S. trials over Phyllis Frances. Felix has been to three Olympics and picked up six medals.