World 800m champion Donavan Brazier failed to qualify for the Tokyo Olympics after finishing last at the make-or-break US trials.
The US record holder, who won gold in Doha in 2019, ran out of energy in the final 200m and finished more than four seconds behind winner Clayton Murphy.
Olympic bronze medallist Clayton set a new world lead of one minute 43.17 seconds, with Isaiah Jewett second.
Brazier, 24, said he “made a move a little too early”.
“I’m very sad. I knew with about 200 left when Clayton passed me and I couldn’t match it,” he said.
“I’m having some things bugging me, but they’re things that someone of championship calibre should be able to push through and nothing that I can make excuses for this race.
“I’ll come back from this. I’ve been down worse before.”
Elsewhere on Monday, world champion and Rio 2016 bronze medal-winning pole vaulter Sam Kendricks reached his second Olympics but had to settle for a two-way tie for second with KC Lightfoot behind Chris Nilsen, who cleared 5.90m.
Two-time Olympic silver medallist Will Claye won the triple jump with 17.21m, capping a remarkable comeback after rupturing his Achilles last year.
“It has been a really difficult year for me,” he said.
Rising star Elle Purrier St Pierre won the women’s 1500m in three minutes 58.03 seconds but Rio bronze medallist Jenny Simpson missed out on her fourth Olympics, finishing 10th in the same race.