Shaunae Miller-Uibo appeared destined to win the women's 400 metres final at the IAAF World Championships, but lost three places in the closing stages as Phyllis Francis won a surprise gold medal at a wet London Stadium.
Olympic champion Miller-Uibo was striding towards the win when she appeared to sustain an injury that opened the door for Francis, as Salwa Eid Naser and Allyson Felix also benefitted to take out the remaining medal places.
Wayde van Niekerk remains on course for an individual double, but only made the 200m final as a fastest loser after clocking 20.28 seconds, while Isaac Makwala put a tumultuous 48 hours behind by advancing after being given a second chance by the IAAF.
Mo Farah did not win his 5000m heat but did more than enough to secure his place in the final, scheduled for Saturday.
FRANCIS PROFITS FROM MILLER-UIBO COLLAPSE
Miller-Uibo was left stunned when she seemed to sustain a late injury in the 400m final and missed out on a medal entirely.
The Bahamian opened up her stride around the final bend but perhaps pushed too hard as she pulled up before the line and finished fourth. Francis of the United States was the chief beneficiary, taking the top step on the podium with a personal best of 49.92secs.
Defending champion Felix had to settle for bronze - a record-equalling 14th medal at the Worlds across her career - as Naser just pipped her to second.
VAN NIEKERK STRUGGLES, MAKWALA THROUGH
Van Niekerk is bidding become just the second athlete to win the 200m and 400m double at the same championships. Although he was visibly fatigued after taking 400m gold on Tuesday, he assured he will be ready for Thursday's final.
"I knew it would be a tough challenge. To see my name in the final is a real pleasure. I've got time to recover now and give it my all in the final," he said.
Makwala was declared medically fit by the IAAF - who pulled him from the 200m heat and 400m final due to illness amid an outbreak of gastroenteritis at a team hotel - and qualified for the semi-finals via a time trial earlier on Wednesday. The world leader returned to the track less than three hours later and finished behind Isiah Young to keep his hopes of a gold alive
There was disappointment for Yohan Blake, though. His time of 20.52s was not enough to join Van Niekerk and Makwala in the event finale.
NO KNEED TO WORRY FOR FARAH
Farah admitted he was struggling with an injury after claiming gold in the 10,000m last weekend but said his knee was fine after qualifying for the 5000m final, in which he will aim to achieve a double success in the long-distance events for the third consecutive Worlds.
"The 10,000m did take a lot out of me but I am okay now. I'm glad I came through tonight and now I can get ready for the final. The knee is fine now, just the body is a bit tired but anything is possible. I just need to recover now and get in the zone," said Farah.
The Brit was beaten by Yomif Kejelcha in the first heat, while Mohamed Sambe was cheered as he crossed the line over two minutes and 45 seconds later. The Mauritanian's time of 16:16.29 was still enough for a personal best, though.
Olympic silver medallist Paul Chelimo suffered a fall in the second half of the second heat but recovered to qualify for the final.
GONG COMPLETES THE SET
After bronze in Berlin and Moscow and silver Beijing, Gong Lijiao's wait for shot put gold is over.
The Chinese threw her fifth attempt 19.94m to win from Anita Marton by 45 centimetres, while Olympic champion Michelle Carter could only do enough for bronze.
In qualification for the men's hammer throw final, Zakhar Makhrosenka produced a wild effort that got caught up in the netting as his campaign came to an end.