Botswana’s Isaac Makwala joined South African favourite Wayde van Niekerk in the World Championships 200m final – having earlier qualified for the semis with a solo run at London Stadium.
Makwala missed Monday’s heats while barred from competing as officials dealt with a norovirus outbreak.
He came out of quarantine at 14:00 BST on Wednesday and ran a time of 20.20 seconds in an individual time trial.
Makwala, 30, then qualified in second place from the first semi-final.
“I wish to thank the IAAF [International Association of Athletics Federations] for giving me another chance, and the crowd is so amazing,” Makwala told BBC Sport.
American Isiah Young won the first semi-final in 20.19secs, with Britain’s Nethaneel Mitchell-Blake finishing third and qualifying in 20.19secs.
Van Niekerk, 25, was running his fifth race in as many days as he looks to add the 200m title to his 400m gold, and he only made it through as a fastest loser.
He finished third in his heat in a time of 20.28secs, but Britons Danny Talbot and Zharnel Hughes failed to qualify.
Starting in lane one in heavy rain, Makwala clocked 20.14secs in his second run of the evening, raising his arm defiantly as he crossed the line.
“I’m still running with the heart broken,” he added.
“I wish the IAAF could take the decision for me to run my 400m first. I was ready to run a 400m alone. Then I can run the 200m.
“The 400m is the race that I’m training for. The 200m I’m doing sometimes.”
Makwala had earlier run alone in lane seven, qualifying with ease before dropping to the track and doing several press-ups after crossing the line to demonstrate his fitness.
Having missed the 200m heats and 400m semi-finals and final, the IAAF allowed Makwala another chance to compete in the 200m after receiving a written request from the Botswanan federation.
“Following a medical examination which has declared him fit to compete, we have agreed under our existing rules that assuming he makes the qualification time, he will run in the 200m semi-final round this evening,” the IAAF said in a statement.
Makwala needed to run a time of 20.53secs or faster to reach the semi-finals.
While individual time trials are uncommon, they have taken place before.
At the Rio Olympics in 2016, the USA women’s 4x100m relay team were allowed by the IAAF to complete a time trial on their own, after protesting that they had been impeded by another team during their heat. They qualified for the final and won the gold medal.