American 16-year-old Cooper Lutkenhaus vowed to come back stronger after being eliminated in the 800 metre heats at the World Athletics Championships on Tuesday, comparing it to "failing a math test".
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The Texas high-school student became the youngest runner to represent the United States at a world championships but made an early exit after finishing seventh in his heat in Tokyo.
Lutkenhaus looked in position to attack with about 150m to go but was unable to break through and crossed the line in 1min 47.68sec.
He took the positives from his performance in front of over 50 000 fans, saying he "came out here just to learn as much as I could and race the best guys in the world".
"It's not your day every time, anybody can tell you that," said Lutkenhaus, who does not turn 17 until 19 December.
"Being in school it's like failing a math test occasionally, but you come back and I'm just excited for what the future holds."
Lutkenhaus punched his ticket to Tokyo with a brilliant effort to finish second at the US trials in Oregon, where he set an under-18 world record time of 1:42.27.
That was the fifth-fastest time over two laps for a US runner.
He could not repeat those heroics in the Japanese capital but said he was "leaving the stadium with my head held high".
"Obviously that's the biggest crowd I've ever raced in front of," he said.
"It was just really cool just to get to step out on that track and see everybody.
"I got to see my family up in the stands, which is something you won't really forget ever."
WANYONYI, AROP QUALIFY
Lutkenhaus said he felt no pressure competing in Tokyo but his presence on the US team has made headlines.
British runner Ben Pattison, who qualified second from Lutkenhaus's heat, said he was forced to do a double take when he saw his young rival's date of birth on the start list.
"It makes me feel old, and me saying I feel old is going to make a lot of other people feel old," said the 23-year-old Pattison.
Kenya's Olympic champion Emmanuel Wanyonyi was among the qualifiers for the semifinals, along with Canada's Paris Games silver medallist Marco Arop.
Lutkenhaus's American teammate Donavan Brazier, the 2019 world champion who has struggled with injury, advanced with the fastest time of 1:44.66.
The lung-busting event has been one of the stand-outs of the athletics circuit this season and David Rudisha's 2012 world record of 1:40.91 could be under threat in Tokyo.
"If a world record falls, that would be amazing," said Arop.
"I hope I can be the one to break, but that's not the goal here."