American seven-time Olympic champion Allyson Felix bowed out from her stellar career with one final World Championship medal, winning bronze in the 4x400m mixed relay in Oregon.
The Dominican Republic denied Felix a golden farewell with the Netherlands pipping the United States to silver.
Felix, 36, retires with 19 world medals, 13 of which are gold.
Elsewhere on day one in Oregon, Great Britain's Laura Muir and Katie Snowden progressed to the 1500m semi-finals.
Muir, who won Olympic silver in Tokyo last year, finished second in her heat in four minutes 7.53 seconds, while Snowden was 10th in her heat in four minutes 6.92 seconds.
"It's always a bit nerve-wracking the rounds, you want to think about the final but you've got to get there first," Muir told BBC Sport.
"It's hard at this level, the strength in depth is really good.
"I was aware there were quite a few of us round there at the end, so I just wanted to stay out of trouble and save as much energy as possible.
"That felt good, that felt comfy."
The semi-finals take place on Saturday, with the final on Monday.
Farewell Felix
World Athletics Championships: Michael Johnson praises Allyson FelixAthletics great Felix announced earlier this year that this season would be her last, culminating at the World Championships - the biggest track and field event to be held in the United States since the Atlanta Olympics of 1996.
The US took the early lead in Friday's final with Elija Godwin on the first leg, with the home crowd in Eugene roaring Felix on as she took the baton.
They slipped down into third on the anchor leg as Fiordaliza Cofil of the Dominican Republic chased down Kennedy Simon, who could then not hold off a late charge from the Netherlands' Femke Bol.
"It was amazing to watch Allyson over the years," former US sprinter and four-time Olympic champion Michael Johnson said on BBC TV.
"I think the thing about her career that has been most impressive is just the longevity.
"Making the US team is very difficult, even just making a relay team, and she has made five Olympic teams, eight World Championship teams, and that's unheard of."
Great Britain's quartet failed to reach the final, having finished fourth at the last edition of the World Championships in 2019.
Bradshaw 'heartbroken' after pole snap
There was disappointment for Britain's Olympic bronze medallist Holly Bradshaw, who was forced to withdraw from the pole vault after landing awkwardly when her pole snapped during the warm-up.
The latest setback came after the 30-year-old missed the indoor season because of "various health, body and mental challenges", having suffered with glandular fever over the winter.
It was the first time Bradshaw has had a pole snap in her career, and she told BBC Sport it was a "very scary experience".
"I wouldn't be surprised if I've torn my hamstring or my glute, and I really hope I've not broken my wrist because that's a long time out," she said.
"I'm heartbroken, this year it's been one thing after another, I can't even tell you how many things have gone wrong, and this is like the icing on the cake. I'm almost having to laugh it off."
Elsewhere for Great Britain, Nick Miller reached the final of the men's hammer throw but Scott Lincoln missed out on a place in the men's shot put final.
In the men's 100m heats, Zharnel Hughes progressed to the semi-finals, finishing second in his heat with the fifth fastest overall time, but fourth in his heat was not enough for compatriot Reece Prescod.
Hughes finished second behind American Fred Kerley, who astonished with his time of 9.79 seconds.
Also making it through to the semi-finals was Africa's fastest man Ferdinand Omanyala, who only landed in Eugene about three hours before his heat after visa issues.
The Kenyan only received permission to enter the United States on Thursday, flying out of Kenya at 18:00 local time that night.
British athlete Chris Thompson will miss Sunday's marathon because of delays processing his US visa.
Organisers said on Friday that less than 1% of athletes in need of a visa had been denied the paperwork to enter the United States or were still waiting for a response.
The first gold medal of the championships went to Peru's Kimberley Garcia Leon in the women's 20km race walk, making history by becoming the first Peruvian to win a medal of any colour at an athletics World Championship.
"I have dreamed of this medal since I was little. I want to dedicate it to all Peruvians," she said.
In the men's equivalent, Japan's Toshikazu Yamanishi defended his title from Doha 2019.
