Eugene (United States) (AFP) - Newly-crowned 100m champion Fred Kerley saw his hopes of a world sprint double go up in smoke Tuesday as he failed to advance from the semi-finals of the 200m.
Kerley set off fine from the blocks but was left grimacing as he hit the home straight at Eugene's Hayward Field, eventually finishing sixth in 20.68 seconds.
Kerley later said he had cramped up in the later stages of the race, but insisted he would be fit to race in the relays.
"Bit of cramp, but it's all good," Kerley said."I'm not in pain, I'll be good."
With Kerley hobbling over the line, the heat was won by the Dominican Republic's Alexander Ogando in 19.91sec.Liberia's Joseph Fahnbulleh was second in 19.92sec.
While Kerley was left digesting a disappointing early exit, there were no such worries for defending 200m world champion Noah Lyles, who romped home in his semi-final with a blistering 19.62sec.
The charismatic American star crossed ahead of team-mate Kenny Bednarek, the Olympic silver medallist, who was second in a season-best 19.84sec.
Lyles's victory was never in doubt after a superb first 100m on the curve that left his rivals trailing.
"It's about time, that's what I've been looking for for a few weeks now," said Lyles of his fast start.
"Not a shock for me but I'm pretty sure it was shock for my competitors."
The main threat to Lyles' hopes of retaining his 200m world title may well come from team-mate and emerging rival Erriyon Knighton.
The 18-year-old prodigy blazed home in the third semi-final in a time of 19.77sec -- a new world under-20 record.
Canada's Aaron Brown finished second behind Knighton in 20.10sec.
Knighton moved effortlessly through the gears to lead coming off the bend and then eased up well before the finish line to book his place in the final.
"I always get out fast, maybe that was about 70 percent on the back stretch," Knighton said afterwards.
The men's 200m final takes place on Thursday.
