“I knew it would be a tough challenge,” Van Niekerk said. “I have time to recover now.”
After two races in one evening, Makwala will need it even more. He was kept out of the 400 final by organizers on Tuesday because of the stomach virus. He also pulled out of the opening heats in the 200 on Monday because of illness.
“I am running with anger,” Makwala said. “The 400 meters is my race. But thanks to the crowd, they were amazing.”
After 48 hours of drama about whether Makwala would be allowed to run any more races at the championships, the International Association of Athletics Federations made an exception and sent Makwala out on his own in driving rain Wednesday evening chasing a mark of 20.53 seconds.
He did it easily, and then got down on the track and did a handful of push-ups as the crowd roared.
Makwala had already qualified for the 400 final when he was a no-show for the 200 heats, suffering from a stomach virus that affected about 30 people at the championships.
Because of the danger to other athletes, the I.A.A.F. kept him out of that 400 final, despite Makwala’s insistence that he was back to full fitness.
“I’m still running with my heart broken,” Makwala said. “I was ready to run.”
In the women’s 400, Phyllis Francis of the United States upset the favorites.
Shaunae Miller-Uibo, the Olympic champion, looked poised to win gold until she slowed in the final meters, seemingly with pain in her right leg.
Salwa Eid Naser of Bahrain swept past Allyson Felix of the United States near the line and lunged for silver.
Francis finished in 49.92 seconds, .14 seconds ahead of Naser. Felix took third in 50.08 and Miller-Uibo was fourth.
“At the finish line I was surprised,” Francis said. “I thought I was second or third. But then they told me, ‘You are first.’ That is crazy.”
Despite her disappointing third-place finish, Felix won her 14th career medal at the world championships. That put her in a tie with Usain Bolt and Merlene Ottey at the top of the career list.
Bolt can still move to 15 with a medal in the 4×100 relay this weekend, but Felix might run on both relay races for the American team, which could bring her to 16.
The biggest surprise on a cold and wet night came in the men’s 400 hurdles. Karsten Warholm of Norway held off Yasmani Copello of Turkey and Kerron Clement of the United States for gold.
Warholm, 21, earned his first major title, and then looked up in amazement as the result showed on the giant screen.
The first gold medal of the night went to Gong Lijiao of China, who won the shot put title ahead of Anita Marton of Hungary and the Olympic champion, Michelle Carter of the United States.
Gong took the lead on her penultimate throw and won with a toss of 19.94 meters. Marton then crept into second position on her last throw, throwing it 19.49 and pushing Carter into third. The American had a mark of 19.14 meters.
Mo Farah, the British star, was back at the Olympic Stadium and got the sellout crowd roaring for his heat in the 5,000.
He ran a controlled race and coasted home in second place to automatically qualify for the final behind Yomif Kejelcha of Ethiopia.
Farah won the 10,000 meters on Friday for his sixth world championship gold and is going for No. 7 on Saturday. It would also clinch his fifth straight long-distance double at a global championships, starting with his double at the Olympic Stadium during the 2012 London Games.