Allyson Felix flew out of the blocks, same as usual. She tried to settle into her rhythm around the turn, as she always has.

Then everything went horribly wrong for the American sprinter. She suddenly screamed and began hopping before falling to the track with a torn hamstring.

There went her world championships. There possibly went her season, too.

As Jamaica's Shelly-Ann Fraser-Pryce won the 200-meter race Friday night, Felix, the Olympic champion in the event, was at the far end of the stadium being tended to by medical personnel.

And as Fraser-Pryce dropped to the track in celebration, Felix was being carried off by her brother, Wes. Felix had big plans, too, possibly winning three medals -- one in her signature event, the 200, along with maybe two more in the 4x100 and 4x400 relays.

"I'm extremely devastated," Felix said in a statement. "I was really hoping to go out there and put together a great race."

It was setting up to be an epic showdown. Fraser-Pryce got off to a fast start, but Felix is known for her finishes.

She never got a chance to kick it into gear.

Suddenly, she was out of the race. From there, it was all Fraser-Pryce as she won in 22.17 seconds. Murielle Ahoure of Ivory Coast was second, a fraction of a second ahead of Nigeria's Blessing Okagbare, a silver medalist in the long jump.

"I heard when she screamed out, but I was really focused on what I wanted," Fraser-Pryce said. "I decided I was running that corner and I didn't care who you were, if you were Usain Bolt behind me, I couldn't care less, I was running like my life depended on it."

The long-term status of Felix remains murky.

"It is a serious injury, but I don't know exactly to what extent," she said. "I wish all of my teammates the best for the rest of the meet."

Felix's fall was one of several did-that-just-happen moments for the Americans.

Earlier, shot putter Ryan Whiting lost out on gold when an official ruling was reversed during the event.

David Storl was at first red-flagged for a foot fault within the circle. The German thrower protested vehemently and a photographer at the scene showed officials pictures of what happened. The official changed his mind and let the winning throw stand.

The U.S. team did not file a protest.

"I'm not going to be bitter about it," said Whiting, who ended up with silver. "I can't fault him for protesting because I would've done the same thing. I would've protested, too. But I don't think I would've let them use the cameraman. I don't think that part is right."

Everything went right for the U.S. 4x400 relay team as the Americans won their fifth straight world title in convincing fashion with LaShawn Merritt strolling across the finish line.

"We went out and got the job done," said Merritt, who also won the 400 on Tuesday. "We train to win."

Everyone else trains to win, too, but rarely are they hurt by their equipment, like Bolt was in a practice session.

The world's fastest man had a clumsy moment in Moscow, dropping the blocks on his foot as he carried them.

No big deal, the Jamaican simply taped his tender right foot and dominated yet again, winning his semifinal heat in the 200.

Even with a bum wheel, he's still nearly impossible to catch. And now he's promising full-out effort for the final Saturday, no letting off the accelerator.

"I'm definitely going to go out there and run," Bolt said. "I'm not going hold anything back. I'm going to go out there and push myself, see how fast I can run."

Watch out world record, Bolt is motivated again. The mark currently stands at 19.19 seconds, his time at the worlds four years ago in Berlin. He's not quite in that type of shape, though.

Of course, anything is possible when Bolt steps into the starting blocks.

And anything is possible when he's carrying them, too.

"Just dropped it on my foot," Bolt said. "It wasn't on purpose. It was just a mistake. I'm not really worried. I'm never worried in the finals. But you never take anybody lightly."

These days, Mo Farah is just as dominant in the distance events as Bolt is in the sprints. Farah added a 5,000 title to his 10,000, giving him another double -- just like at the London Olympics.

The other runners even tried to take the race out at a faster pace, but it didn't work.

"It suited me so it was a great race," Farah said. "I had a (cramp) from about eight laps to go and I was kind of pushing my stomach in, but then the pace slowed down and I tried to forget about it and come through."

In other finals, Aleksandr Menkov of Russia won the men's long jump title, with four-time champion Dwight Phillips 11th. Olympic champion Tatyana Lysenko of Russia captured the hammer throw.

There are two days still to go at the world championships, and two women's relays remaining. Felix had been planning to run in both.

That's not going to happen.

"This is life, man. Things happen in life," Merritt said. "That is just the way things go. Nothing is always going to be perfect."