Wayde van Niekerk retained his world 400 metres title in dominant fashion on Tuesday as he stormed to victory in 43.98 seconds but there was almost as much interest in the empty lane alongside him where Botswana's Isaac Makwala should have been.
South African Van Niekerk, the Olympic and defending champion and world record holder, ran a controlled race and was even able to ease down over the final strides as he secured the first half of what he hopes will be a 400/200m double.
Steven Gardiner, 21, of the Bahamas was a clear second in 44.41 and 20-year-old world junior champion Abdalelah Haroun of Qatar blasted through at the end to snatch bronze in 44.48.
Makwala, third-fastest in the year this season, was scratched from the race earlier on Tuesday having also been withdrawn from Monday's 200m heats after vomiting before he got on to the track.
He insisted he wanted to run but IAAF officials ruled him out for public health reasons and refused him entry to the stadium amid a swathe of nanovirus and gastroenteritis cases that have affected about 30 athletes from a selection of countries.
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In his absence, Van Nierkerk looked an even shorter-odds favourite and duly delivered, barely seeming out of breath when he crossed the line with his thoughts already turning to the 200m.
"I've got a good team to help me recover and its back to work tomorrow," he said.
Van Niekerk had huge sympathy for Makwala.
"It was definitely a heartbreaking moment," he said. "I saw him just before the 200 heat and the only thing I could think of was just wrapping my arms around him and telling him he should get well soon.
"As much as we want to win gold medals, we also want to go out there and have best guys on the track with us. It's such a massive pity. He's a strong athlete, I've seen him break through a lot of challenges. So I have a lot of sympathy for him.
"I wish I could give him my medal to be honest, but this is sport. We need to go out there and fight for our opportunities and it could've happened to any one of us."
Meanwhile, Pierre-Ambroise Bosse took gold in the men's 800m in one minute 44.67 seconds, ahead of Poland's Adam Kszczot and Kipyegon Bett in third.
The Czech Republic's Barbora Spotakova also took the javelin title ahead of Lingwei Li after throwing 66.76m to regain the crown 10 years after first winning it in Osaka.
Conseslus Kipruto also claimed the 3,000m steeplechase crown ahead of Soufiane Elbakkali and the USA's Evan Jager.
