The United States captured a third athletics gold of the evening when world indoor and outdoor champion Brittney Reese took the women's long jump, despite making only two of six jumps all night.
Russia's Natalya Antyukh just held on at the line to beat American Lashinda Demus in the women's 400 meter hurdles.
In other action on Day 12 of the Games, Hungary claimed men's and women's canoeing titles and Steve Guerdat of Switzerland won individual show jumping gold.
China completed a second successive sweep of all Olympic titles in table tennis when its men's team beat South Korea 3-0.
French and Spanish basketball players nearly came to blows, while Italy's men knocked out defending champions the United States in volleyball and Hungary in water polo.
Eighty thousand spectators in the Olympic Stadium witnessed the latest installment in a series of US-Jamaican track showdowns, with the Americans this time coming out on top.
Felix, a silver medalist at the last two Olympics, strode out in the home straight to beat Shelly-Ann Fraser-Pryce, the Jamaican winner of the 100 meters, with Carmelita Jeter of the United States taking bronze.
“It's been a long time coming. I've waited so long for this moment,” Felix said.
Jamaican Veronica Campbell-Brown, bidding for a third straight Olympic 200 meters title, came fourth.
The high hurdles was another US-Jamaican affair, with Americans Merritt and Jason Richardson taking gold and silver, while Hansle Parchment got the bronze.
American Ashton Eaton opened his bid to become the best all-round male athlete of the Games with a 10.35-second 100 meters dash and long jump of 8.03 meters that put him in the lead of the decathlon.
Sarah Attar became the first woman from Saudi Arabia to compete in the Olympic athletics, coming last in an 800 heat she ran wearing a white head cover.
“It is the hugest honour to be here to represent the women of Saudi Arabia. It is an historic moment. I hope it will make a difference. It is a huge step forward. It's a really incredible experience,” said Attar, who also has US citizenship and is a student at Pepperdine University in Los Angeles.
Compatriot Wojdan Ali Seraj Abdulrahim Shaherkani similarly bowed out at the first hurdle, lasting just 80 seconds on the judo mat last week, but the pair have been hailed as heroines by many in their homeland and around the world.
Russia's 30-year-old double Olympic champion and world record holder in the women's pole vault, Yelena Isinbayeva, told Reuters on Wednesday she would compete again in Rio de Janeiro in 2016 having come a disappointing third in the London Games.
Her compatriot Ivan Ukhov revealed that he had been forced to borrow a T-shirt from a team mate to make his winning leap in the men's high jump on Tuesday after his own vest was stolen midway through the competition.
It may even have helped. The shirt belonged to fellow Russian and 2008 Olympic champion Andrei Silnov.
“I guess Andrei being the 2008 champion just passed me the good luck,” Ukhov told Russian media.
Ireland's Katie Taylor beat a Tajik opponent to set up a women's lightweight boxing final against Russia's Sofya Ochigava. In the middleweight final, 17-year-old Claressa Shields of the United States was to face another Russian, Nadezhda Torlopova, who at 33 is nearly twice her age.
The US men's boxing team left the Olympics without a medal for the first time. “They weren't worth watching, every single one of them was garbage,” multiple weight world champion James Toney told Reuters.
Spain broke open a fierce defensive battle in the final minute to beat France 66-59 and reach the semifinals of the Olympic men's basketball tournament in a bad-tempered contest that threatened to turn into a brawl.
“Everybody wants to fight for those medals. Sometimes it gets a little out of hand because emotions get involved. Nobody got hurt, that's the most important thing,” Spain's Marc Gasol said.
Three-quarters of the way through the Games, International Olympic Committee president Jacques Rogge said he was satisfied with the way they had gone so far.
“All in all I would say these are very good Games and I am a very happy man,” he told reporters.