Botswana's Isaac Makwala will go for World Championships gold after overcoming illness, quarantine and two races in little more than two hours to qualify for Thursday's 200 metres final.
Makwala was on Tuesday night denied the chance to face South Africa's Wayde van Niekerk, the world and Olympic 400m champion, over one lap.
The 30-year-old, who was told he could not take up his place in the 400m final on medical grounds following illness, clocked 20.14 seconds to place second in the first semi-final heat in torrential rain at the London Stadium.
Makwala was an additional athlete in the semi-final heat, running in lane one - not normally used for the event due to the tightness of the bend - after qualifying via a time-trial earlier on Wednesday evening.
He qualified for Thursday's final behind the United States' Isiah Young, who won the semi-final as Makwala celebrated by raising his right arm aloft.
Britain's Nethaneel Mitchell-Blake finished third in 20.19 and had to wait to see if he would be one of two fastest losers from the three semi-final heats.
Meanwhile, American Phyllis Francis won the World Championships 400 metres final as Olympic champion Shaunae Miller-Uibo stumbled when seemingly certain of victory and dropped to fifth place.
Francis looked out of it with 80 metres to go but maintained her form amid the carnage to post a personal best time of 49.92 seconds and take a shock gold medal.
Bahrain's Salwa Eid Naser, 19, claimed a brilliant silver in 50.06secs as defending champion Allyson Felix of the United States faded to get bronze in 50.08.
Bahamanian Miller-Uibo, who famously dived over the line to pip Felix to Olympic gold last year, was clear with 20 metres left but as she tired and tied up she tripped on her own foot, stumbling almost to a standstill as her rivals stormed past her.
Felix's bronze took her world championship medal haul to 14, matching the record of Jamaican sprinters Usain Bolt and Merlene Ottey. The American's tally includes nine golds.