Britain's Lisa Dobriskey qualified for Saturday's final of the women's 1500m after a strong finish helped her finish third in her semi-final.
The 22-year-old from Kent clocked four minutes 03.22 seconds to progress but fellow Britons Stephanie Twell and Susan Scott both missed out.
Michael Rimmer failed to reach the final of the 800m after finishing sixth in his semi-final in 1:48.47.
"I felt like I had nothing in my legs," the 22-year-old told BBC Sport.
"Every time I run, I run hard," Rimmer added. "But as soon as we set off, I knew I was in trouble.
"They went off fast but I am quick and I should have been able to keep up. I felt terrible all the way round."
The defending champion, Russia's Yuriy Borzakovskiy, was another who failed to progress and two of the favourites - Uganda's Abraham Kewmoi Chepkirowok and Sudan's Abubaker Kaki - also crashed out.
Dobriskey, however, ran a perfect race to come through on the home straight and finish third.
I am really pleased," Dobriskey told BBC Sport. "I saw the first and second semi-finals and they were quite quick so I had to stay relaxed and calm."
The first three from each of the three semi-finals qualified automatically, along with the three fastest losers.
Bahrain's Maryam Yusuf Jamal, the world champion, and the Ukraine's Iryna Lishchynska - who was third in Osaka in 2007 - both joined Dobiskey in the final.
Twell, the world junior champion, finished sixth in the first semi-final but clocked a fast time of 4:06.68 and was in contention to go through until Dobriskey's race.
Scott finished fourth in the second semi-final but in a much slower time of 4:14.66.
Britain's Daniel Awde ended a disappointing first day in the decathlon on a high note by posting a personal best of 47.16 secs in the 400m - the fastest of any of the 36 competitors.
But Awde is down in 26th overall after finishing last in the shot putt with 12.03m and also in the high jump with a mark of 1.78m. He was also 17th-fastest in the 100m (11.06 secs) and 18th-best in the long jump (7.12m).
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