Dina Asher-Smith missed out on a 100m medal at the World Championships in Budapest as American Sha'Carri Richardson beat a star-studded field of rivals to claim her first major title.
Britain's Asher-Smith finished a disappointing eighth in 11.00 seconds after scraping through the semi-finals.
Richardson, contesting her first major final at 23, clocked a championship record 10.65 secs to take victory.
Jamaica's Shericka Jackson took silver ahead of Shelly-Ann Fraser-Pryce.
Jackson, the reigning 200m champion, ran 10.72 secs as compatriot and record five-time champion Fraser-Pryce finished in 10.77.
Three-time individual world medal winner Asher-Smith, who was crowned 200m champion in 2019, was left unsure as to why she could not perform at the level she expected.
"I'm almost in disbelief. I know myself and I know that I feel good. I came here for a new personal best," she said.
"I know I'm in great shape. It doesn't really happen to me - that's why I'm so surprised."
The 27-year-old has made a habit of producing her best at major championships, but her participation in the final was initially unclear after a unconvincing run in the semis earlier in the session.
Asher-Smith appeared to have qualified for the medal race as the last non-automatic qualifier by one thousandth of a second.
But Poland's Ewa Swoboda was then also permitted to contest the final by organisers due to the miniscule difference between the times set by the two, leaving nine athletes in a stacked race featuring the six fastest women in the world.
In the final it was Richardson - competing at her first major championship after missing the Tokyo Olympics through suspension and failing to qualify for last year's Worlds - who prevailed, greeting victory with joyous celebrations.
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Richardson shocks the world - and herself
At first, Richardson simply could not believe it.
Inexperienced at this level, she had failed to secure automatic qualification after finishing behind Jackson and Marie-Josee Ta Lou in her semi-final.
But, as the battle for gold appeared to be focused on a blur of yellow and green as the Jamaican duo Jackson and Fraser-Pryce duked it out in the centre, Richardson stole in from lane nine.
The stunned American almost stumbled over the edge of the track as she backpedalled in an attempt to get a better look at the big screen, waiting for confirmation of the result she longed to see.
When it arrived she was overcome with emotion before bursting into celebration, running around the track with an American flag raised above her head.
Following a turbulent start to her senior career, in which she was suspended for an anti-doping rule violation for the use of cannabis, a determined Richardson has insisted this season: "I'm not back, I'm better."
In Budapest, she proved that in the most emphatic way.
Puzzling disappointment for Asher-Smith
Achieving a medal always appeared a tall task for Asher-Smith, even on her very best day.
The signs were not good in the semi-finals, with something evidently not right as she faded following a positive start to place third - outside of the automatic qualification places.
One year after she missed out on world 100m bronze by 0.02 secs, it appeared she had fallen on the right side of a narrow margin this time, until an allowance was made for the unfortunate Swoboda to race too.
But there was to be no miraculous turnaround in the final, and she must now look ahead to ensuring she is ready for the 200m heats on Wednesday.
"Towards the end of the semi-final I just couldn't feel my legs anymore, which was a bit strange," Asher-Smith said.
"I don't want to make a huge deal because at the end of the day I crossed the line, felt fine, got on with it, made the final, and felt absolutely fine during the final.
"I felt great but [it was] a mad day, mad day."
Team-mate Daryll Neita saw her World Championships end in the semi-finals for a second successive year as she finished fourth in her heat in 11.03 secs.
Who else won medals on day three?
Elsewhere, American Grant Holloway won his third successive 110m hurdles world title in a time of 12.96 secs.
Sweden's Olympic champion Daniel Stahl clinched his second gold at a World Championships in a gripping discus competition, pipping Slovenia's defending champion Kristjan Ceh with the final effort of the event - a championship record of 71.46m.
In the men's triple jump, Hugues Fabrice Zango won Burkina Faso's first world gold with a jump of 17.64m, after highly-rated 18-year-old Jamaican Jaydon Hibbert pulled out with a hamstring injury sustained on his first jump.
Norwegian Olympic champion Karsten Warholm eased into the final of the men's 400m hurdles in a time of 47.09 secs, while Great Britain's Jessie Knight impressively made the semi-finals of the women's event by winning her heat in 54.27 secs.
That was still well behind the pace of Netherlands' Femke Bol who recovered from her fall in the 4x400m mixed relay to cruise through from her hurdles heat in 53.39 seconds.
An emotional Holly Bradshaw failed to qualify for the women's pole vault final but British champion Molly Caudery did make it through, clearing the automatic qualifying height of 4.65m at the third attempt.
Fellow Britons Tade Ojora, in the men's 110m hurdles, and Victoria Ohuruogu and Ama Pipi, both in the women's 400m, went out in the semi-finals of their events.