World champion Donavan Brazier's Olympic dreams were shattered on Monday as the overwhelming favourite in the men's 800 metres suffered a shock defeat at the U.S. trials.

The 24-year-old American record holder seemed all but assured a spot on Team USA heading into Eugene, Oregon, this week but ran out of gas with 200 metres to go, finishing dead last with a time of 1:47.88 as he was forced to relive the disappointment of the 2016 trials, where he also came up short.

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Clayton Murphy, 26, who picked up bronze at the Rio 2016 Olympics, won in a blistering, world-leading 1:43.17. Isaiah Jewett, 24, finished second with a personal best of 1:43.85.

Earlier in the day, athletes arrived on the track wearing ice vests to combat the ferociously hot conditions, with temperatures hovering around 93 degrees Fahrenheit (33.9 degrees Celsius) as the action kicked off inside Hayward Field.

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Pole vaulter Sam Kendricks, 28, who won at the World Championships in Doha in 2019 and claimed Olympic bronze five years ago, booked his ticket to Tokyo after finishing second behind 23-year-old Chris Nilsen, who cleared 5.90 metres.

Kendricks had won consecutive U.S. national championships from 2014 through 2019.

Elsewhere in the day's action, rising star Elle Purrier St. Pierre, 26, clinched the 1,500m in 3:58.03, while 2016 bronze medallist Jenny Simpson, 34, came up short in her bid for a fourth trip to the Olympics, finishing tenth.