• American unlikely winner after Miller-Uibo pulls up on the home straight • Miller-Uibo looked to have strained a muscle in her right leg

Shaunae Miller-Uibo has a propensity for producing dramatic finishes to 400m finals. At the Rio Olympics it was a controversial dive over the line to take gold and in London her breakdown with 20 metres to run was equally bizarre.

She was in charge and cruising down the home straight but suddenly lost her stride after apparently pulling a muscle in her right leg. It opened the door for Phyllis Francis to win gold in one of the shock results of the championships.

The race had been billed as a rematch between Miller-Uibo, from the Bahamas, and the American legend Allyson Felix, beaten into silver in Rio by that unorthodox dive. The idea that neither would occupy the top two places on the podium was almost unthinkable.

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The first half of the race unfolded as per the script with both women coming off the final curve ahead but the 6ft 2in Miller-Uibo used her long stride to move away until disaster struck. Francis held her form to clinch victory in a personal best 49.92sec with the 19-year-old Salwa Eid Naser of Bahrain taking silver in a national record 50.06, narrowly beating Felix. After the race the 23-year-old Miller-Uibo was swiftly helped to the medical room, without stopping to explain what had happened.

“I didn’t see what happened to Shaunae,” Francis said. “My goal was to come in the top three, to just stay with Shaunae and Allyson who I knew would set the tone.”

Felix said before the race she was “hungrier than ever” which is some claim given she has competed at every world championships since Helsinki in 2005. Her bronze, while not the colour she desired, is a record equalling 14th world medal, a feat shared by Jamaican sprinters Usain Bolt and Merlene Ottey. But disappointment was her prevailing emotion.

“It didn’t exactly go how I hoped,” she said. “You always go into a race wanting to win, that was my goal all season so when you fall short there’s definitely disappointment. I feel so grateful to still be competing at the top but I’m definitely sad.”

The men’s 400m hurdles also produced a surprising result as the 21-year-old Norwegian Karsten Warholm won gold, beating Turkey’s Yasmani Copello and the Olympic champion Kerron Clement.

A former decathlete, Warholm led from the first hurdle and held off his rivals on the home straight to win in 48.35sec, clasping his face in shock as he crossed the line. Copello took silver in 48.49 with the race favourite Clement settling for bronze in 48.52. Wearing a baseball hat, Abderrahman Samba of Qatar was in medal contention until hitting the final hurdle and stumbling home in seventh.

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Warholm completed his lap of honour draped in the Norwegian flag and wearing a plastic medieval Viking helmet to celebrate the country’s first track world gold since Ingrid Kristiansen won the 10,000m in Rome in 1987.

“I truly don’t believe it,” he said. “I’ve worked so hard for this but I don’t know what I have done. This is an amazing feeling. I’m world champion, that’s crazy.”

China’s first gold of the championships was claimed in the women’s shot put by Lijao Gong who threw 19.94m. “It is 26 years since China won a shot put medal,” she said, “so it’s a very special moment for me. Of course, the rain affected the competition and that is the reason we didn’t go past 20 metres.”

Great Britain are still looking to add to their medal tally. Nick Miller is being quietly talked about as a potential podium prospect in the men’s hammer and he looked the part when he qualified with his first throw of 75.52m.

“Job done,” he said. “That was the plan, just take a nice easy throw, confident, and walk away. I felt good, I’m in good shape, I just wanted to do myself proud.

“Last year I had a stress fracture in my spine and I kind of went into Rio knowing it was a long shot but now I’m healthy and things are looking good.”

“This year is a new year and now I’m here, I’m ready to play. It’s a great crowd at the London Stadium – I can hear my dad whistle. It’s great to know my family is here supporting.”