Rhasidat Adeleke is through to the women's 400m final after finishing second, so securing an automatic place in Friday's medal race.
With the top two in each of the three heats advancing plus the two fastest losers, Adeleke just about did enough to hang on for second place, as Bahrain's Salwa Eid Naser ran out an impressive winner in 49.08, with the Tallaght competitor clocking 49.95.
Adeleke did not seem as fluid on the home straight as during her heat, but held on to finish ahead of Henriette Jaeger of Norway, who was .22 of a second behind the Irish record holder.
The 2019 world champion, Naser missed the 2022 worlds and Tokyo Games after she was hit with a two-year ban in 2021 for an anti-doping violation and an injury sidelined her for last year's World Championships in Budapest.
Adeleke's time was the sixth fastest of the eight across the three heats. She will run in lane four on Friday, with Great Britain's Amber Anning immediately outside her in lane five.
The opening heat did see a recall and restart, with the Netherlands' Lieke Klaver given a warning and Adeleke admitted that had an impact on her performance with a further wait to get going.
"That was a very messy race," she told RTÉ Sport's David Gillick afterwards.
"I was ready to go (before the false start), but when we went again I felt like I was thinking about it too much. I didn’t execute my first 200m like I should have, but that’s nothing that can’t be fixed for the final.
"I think I also panicked a little bit which made me break form really early. I’m excited, I’ve made the final and now I can give it my best shot."
After struggling to match her opening performance in Paris in the 400m heats, the 21-year-old says she is able to draw on previous experience when channelling her focus on the main event.
"I’ve been in that place where the rounds might not have gone how I wanted to, but the final went great, so I’m not too worried about it," she said.
World champion Marileidy Paulino won the second heat in a time of 49.20, ahead of the USA's Alexis Holmes in 50.00, following another recall.
In the final heat, European champion Natalia Kaczmarek just edged out Amber Anning on the line, in times of 49.45 and 49.47 respectively as they both claimed their automatic spots in the final.
The fastest woman in the world this year, Nickisha Pryce, as well as Klaver, failed to make the final.
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