Allyson Felix of the U.S. celebrates after she won gold in the women's 200m final during the London 2012 Olympic Games at the Olympic Stadium (Photo: Reuters)
She ran a good bend but with Jamaican's Veronica Campbell-Brown and Shelly-Ann Fraser-Pryce still in medal contention, Felix lengthened her stride down the home straight for victory in 21.88 seconds.
"It's been a long time coming. I am so overjoyed," said Felix, who was runner-up to Campbell-Brown in 2004 and 2008 and lost her world title to the Jamaican last year.
"I thought back to the disappointment in Beijing, it's been a long road, I never wanted to give up," the 26-year-old told reporters.
"I've wanted it for so long. This moment is really priceless."
Olympic 100 metres champion Fraser-Pryce of Jamaica took the silver in 22.09 ahead of American Carmelita Jeter, who won the bronze in 22.14.
Campbell-Brown faded down the home straight to finish fourth (22.38) with Olympic 400 champion Sanya Richards-Ross in fifth.
"We've been racing each other for years. I'm happy for her. I knew how bad she wanted it," Campbell-Brown told reporters.
A beaming Felix, who has a record eight world championship golds, jogged her lap of honour holding the U.S. flag as the nation claimed three athletics golds in the session.
Brittney Reese won the women's long jump title and Aries Merritt the 110 hurdles.
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