MOSCOW — 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 being tended to by medical personnel.
‘‘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.
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. The long-term status of Felix remains murky.
‘‘It is a serious injury, but I don’t know exactly to what extent,’’ Felix said. In other events, American shot putter Ryan Whiting lost out on gold when an official ruling was reversed during the event. German David Storl was red-flagged for a foot fault but officials reversed their decision after viewing photos.
Everything went right for the US 4 x 400 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.’’
Mo Farah added a 5,000 title to his 10,000, giving him another double — just like at the London Olympics.
Also Friday, Russian pole vaulter Yelena Isinbayeva backed off on comments made a day earlier in support of her country’s new anti-gay laws. “Let me state in the strongest terms that I am opposed to any discrimination against gay people,’’ she said in a statement.