Wayde van Niekerk retained his world 400 metres title in dominant fashion 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Makwala, third-fastest in the year this season, was scratched from the race earlier today having also been withdrawn from yesterday's 200m heats after vomiting before he got on to the track.
He insisted he wanted to run but IAAF officials ruled him out 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.
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.
Long-striding Gardiner, who set a national record 43.89 in the semis, could not quite reproduce that on a cold London night but looks equipped to challenge Van Niekerk in the future.
Haroun, who switched nationality from Sudan to Qatar two years ago, edged past Baboloki Thebe of Botswana and Jamaica's Nathon Allen in the final metres.
Fred Kerley had scraped into the final as a fast loser but finished last as the United States failed to medal in the event for only the second time since the championships began in 1983.
Elsewhere Pierre-Ambroise Bosse of France took gold in the men's 800m, the Czech Republic's Barbora Spotakova took the javelin title, Kenya's Conseslus Kipruto claimed the 3,000m steeplechase crown and American Sam Kendrick took gold in the pole vault.