Allyson Felix raced to Olympic 200m gold in a time of 21.88 seconds, to win the title at the third attempt.
The three-time world champion beat a strong field to register her first Olympic gold over the distance after two silvers in 2004 and 2008.
The American came from behind in the
final straight to pip Jamaican Shelly-Ann Fraser-Pryce to first place.
"That was very impressive from Allyson Felix. It was a great race with some great athletic talent. Felix, with her long stride, is a great sprinter with very nice technique. She could not be matched."
Fraser-Pryce ran a personal best 22.09 to take silver, with Carmelita Jeter of the United States third in 22.14 secs.
"It has been a long time coming," said Felix. "I've waited so long for this moment and I am just overjoyed. There are so many people I love here tonight and I am just overjoyed to share it with them."
Veronica Campbell-Brown, who won the title in 2004 and 2008, finished outside the medal placings in fourth.
The Jamaican duo of Fraser-Pryce and Campbell-Brown got off to a flying start, leaving the rest of the athletes trailing. But Felix, in lane six, finished the stronger, while Fraser-Pryce held off Jeter to take second.
Felix, 26, went into the race buoyed by the fastest time in the semi-final, having been the only athlete to run under 22 seconds.
She took that form into the final to banish her disappointment of previous years against a high-class field in which London 2012's
400m champion Sanya Richards-Ross