Athing Mu lost the chance to defend her Olympic 800m title in Paris after crashing to the ground and trailing home last at the US trials on Monday, while Quincy Hall upstaged Michael Norman to win the men's 400m in Eugene, Oregon.
Mu beat Keely Hodgkinson to gold in Tokyo three years ago, as the British runner settled for silver.
The trials had largely gone to script on the first three days but Mu’s calamity stunned the crowd at Hayward Field.
The 2022 world champion and hot favorite tripped around the 200m mark and while she bravely carried on she had no chance of catching up to the field.
Nia Akins (1:57.36) came home first while Allie Wilson (1:58.32) and Juliette Whittaker (1:58.45) also earned their place in the event.
Hall put on the best performance of his career as he chased down 2022 world champion Norman after the final turn to win the 400m in 44.17.
Norman paid the price for going out too quickly, losing steam down the home stretch to finish in 44.41.
“I know I can run a lot faster than what I did today. Just a poorly executed race,” Norman said. “Kind of got a little too excited during the moment so I paid for it at the end.”
Chris Bailey took third in 44.42 while high school phenom Quincy Wilson finished sixth and could earn a call-up for the relay pool at just 16-years-old.
Grant Holloway sent a message to his rivals with a blazing fast opening performance in the 110m hurdles, winning his heat in a world-leading 12.92.
The three-time world champion took silver in Tokyo but made it clear he would accept nothing but gold in Paris.
“I just wanted to put pressure on the field, let everybody know that I'm still on top,” he told reporters.
Anna Hall closed out her heptathlon triumph with a superb 2:04.39 in the 800m and collapsed to the track in celebration as Jackie Joyner-Kersee, who won gold in the event in Seoul and Barcelona, watched from the stands.
Hall will look to add an Olympic gold to her world championships silver and bronze, with Chari Hawkins and Taliyah Brooks traveling to Paris as well.
World indoors silver medalist Cole Hocker won the men's 1,500m in 3:30.59 and will be joined on the team by Yared Nuguse (3:30.86) and Hobbs Kessler (3:31.53).
Elle St Pierre held off Elise Cranny down the home stretch to win the women's 5,000m in a meet record 14:40.34, with Karissa Schweizer finishing third.
The US Olympic trials will resume on Thursday with the 100m winners Noah Lyles and Sha'Carri Richardson expected to compete in the opening heats of the men's and women's 200m.
