Great Britain fell short of a first medal on the opening day of the World Athletics Championships in Tokyo with a fifth-place finish in the mixed 4x400-metre relay final.
The Brits were second-fastest in the two morning heats after a blistering anchor leg from Yemi Mary John, who was replaced by Emily Newnham in the lineup to run alongside Lewis Davey, Toby Harries and Nicole Yeargin.
Yeargin said: "I knew I should have taken them on the back stretch. I was going too slow.
"I almost stepped on Femke twice, on her heels. I knew we were going too slow. I was hoping I'll catch them in the end but I should have trusted myself to go earlier."
Great Britain will have a full complement of men's 100-metre semifinalists after Jeremiah Azu, Zharnel Hughes and Romell Glave all booked places from the heats.
And it was the same story for their female counterparts as Daryll Neita, Dina Asher-Smith and Amy Hunt all automatically qualified.
These championships were billed as an atonement and reward for Japanese fans, who expected to welcome the world to their Olympics in 2020.
But COVID-19 had other plans for Tokyo and those Games were postponed a year, then eventually played out in front of empty stadia.
Saturday's first evening session was sold out, with Japan's Crown Prince and Crown Princess Akishino among guests of honour alongside governor of Tokyo Yuriko Koike and IOC president Kirsty Coventry.
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The mixed 4x400-metre relay was the final event of the evening session.
Great Britain claimed silver in the same event at the last World Championships in Budapest and bronze at the Paris 2024 Olympics but were unable to recreate that success in Tokyo, finishing fifth in three minutes 10.84 seconds.
The United States took gold in 3:08.80, the introduction of reigning world 400-metre hurdles champion Femke Bol propelled the Netherlands to silver and Belgium collected bronze.
Welshman Azu, who was disqualified for a false start in the heats on his Olympic debut in Paris, this time booked his place in the 100-metre semifinals in 10.10 seconds.
Hughes was second in heat six, clocking 10.06 seconds, while Glave had to sit through six heats to confirm he was one of the three best-of-the-rest going through.
Hughes said: "I know when I get to the semifinals I have to step it up, and I will step it up."
Neita set a season's-best 10.94 seconds to win the fifth of the women's 100-metre heats, and emerged the second-fastest from all seven heats behind St. Lucia's Olympic champion Julien Alfred.
Asher-Smith and Hunt were second in their heats in 11.07 and 11.13 seconds respectively.
"Happy and excited to get started," Asher-Smith said. "I have been out here for a while and I have just been waiting and waiting. That was a good run for me."
Shot putter Scott Lincoln qualified for his first world final on Saturday morning, ultimately finishing eighth with a best attempt of 21-metres as American Ryan Crouser defended his title for a second time with a season's-best 22.34.
Megan Keith and Calli Hauger-Thackery finished 10th and 11th in their 10,000-metre final.
Revee Walcott-Nolan booked her place in the women's 1500-metre semifinal but debutant Erin Wallace and Tokyo 2020 silver medallist Laura Muir missed out.
Long jumper Jazmin Sawyers -- who recently returned to action following a 20-month Achilles injury absence -- needed to finish in the top 12 to advance but came 16th.