MOSCOW (AP) -- Ashton Eaton of the United States ran a blistering 400 meters to regain the lead after the first five events of the decathlon Saturday, while defending champion Trey Hardee dropped out with a hamstring injury at the world championships.
The world-record holder clocked 46.02 seconds to run the fastest decathlon 400 at a world championships, according to the IAAF.
Eaton holds with a slim lead of 4,502 points to American Gunnar Nixon's 4,493. Michael Schrader of Germany fell to third with 4,427.
The start of the grueling two-day event shaped up as a thrilling showdown between two Americans, Eaton and the 20-year-old Nixon. Hardee, the two-time defending champion and Olympic silver medalist, failed to earn points in the high jump and withdrew.
Hardee developed cramps in his hamstring and missed all three high jump attempts. He was fifth after three events and needed a good performance in the high jump to stay in medal contention.
"It was just one of those things, landed on the pit after my second attempt, my hamstring was grabbing," Hardee said. "I laid there and tried to keep it from cramping up. The third (attempt) came around way too quick."
Nixon, the junior world champion, cleared 7 feet, 1-4 in the high jump to seize a big lead after four events. But Eaton surged back with his fast 400, only 0.39 seconds off his personal best.
Nixon had led Schrader by 110 points and Eaton by 116 after the high jump.
Eaton held the lead after the first three events but cleared only 6-4 in the high jump, his season best nevertheless.
"The high jump is definitely rusty," Eaton said. "For the long jump and shot put and high jump, think I was just lacking motivation. I think it was a long three years (competing).
"Later on down the road, I'm going to have to get my act together if I want to beat him. For a 20-year-old at world champs to be in the medal hunt, that's very good for the future of Gunnar and the U.S. decathletes."
Schrader cleared a personal-best 6-6 1-4. But the high jump belonged to Nixon, who even tried 7-1 1-2 despite already being in the overall lead. However, he failed in all three attempts.
Hardee said he tried to work out the hamstring injury.
"I could jog fine, thought, this will be OK," Hardee said. "I was trying to summon some energy, trotted down and it wasn't letting me run. The more open my gait became, the more I used it, the more it wanted to stop and cramp up."
Eaton broke the world record at the U.S. Olympic Trials with a score of 9,039 last year, before confirming that performance with a gold medal at the London Olympics.
The American came to Moscow at 13th place on the world list, with a season-best of 8,291 points for the title at the U.S. nationals.
But he also set personal bests in five events.
Nixon's top performance is 8,198 points in finishing second to Eaton at the U.S. nationals.
"I'm right where I want to be. I'm out there having fun," Nixon said. "I had two personal bests today in the long jump, shot put, an overall Day 1 personal best.
"I'm out there having fun. No pressure. Trying to do my best in each event."
The decathlon ends Sunday after the remaining five events.
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