BEIJING (AP) — Long after two of the all-time greats at 400 meters had left the track in second and third place, the winner was sprawled on the ground, gasping for breath and getting his pulse checked by a medic.

This is how 23-year-old Wayde van Niekerk of South Africa made a name for himself at the world championships Wednesday night, while also inserting that name on the "People to Watch" list for next year's Olympics in Rio de Janeiro.

A muggy evening at the Bird's Nest started with Usain Bolt laughing as he cruised into the finish of his winning 200-meter semifinal heat to set up another gold-medal showdown with Justin Gatlin. It ended with van Niekerk topping two Olympic and world champions, LaShawn Merritt and Kirani James, before being carted off the track on a stretcher, then loaded into an ambulance.

Van Niekerk was taken to the hospital for precautionary measures, then released later in the evening.

"He told us he was going to make mincemeat out of them," said the chairman of the South African track team, Pieter Lourens.

He did.

In many ways, the 400 is the most brutal race of them all — basically a sprint, but one in which the sprinter has to also focus on tactics and conserving energy during a 40-some-second trip around the track.

Van Niekerk didn't worry much about that last part.

Running out of Lane 6, he had already made up the lag to the runner on his right, Luguelin Santos, after the first 50 meters. And by the time van Niekerk hit the straightaway, there was a bathtub-sized chunk of daylight between himself and Merritt.

Front-runners like that often fade late, but this one didn't. Van Niekerk finished in 43.48 seconds, the sixth-best performance of all time. He won by .17 over Merritt, the 29-year-old, two-time world and 2008 Olympic champion, who himself posted a personal best.

Wouldn't he expect to win the gold medal with that sort of time?

"If you'd said I'd run 43.6, I'd say, 'Yeah,'" the American said. "To go under what I got under, it's a great race. He came out and ran well. We're animals. We're warriors."

Merritt raised two fingers after the race, happy to have finished second to top off what he called a "rough" season.

On yet another disappointing night for the Americans, second was the best they could manage.

Shamier Little and Cassandra Tate finished 2-3 in the 400-meter hurdles to round out the U.S. haul and bring the total to nine medals over the first five days of the championships.

There's only one gold in that mix, which leaves the United States a surprising five wins behind the leader, Kenya.

The day actually started off with bad news for Kenya, when a hurdler and a 400-meter runner from the country were suspended for doping. It ended much better thanks to wins by Hyvin Kiyeng Jepkemoi in the women's steeplechase and Julius Yego in the javelin. Yego's throw of 92.72 meters was the longest in 14 years and gave the country known for great long-distance running its first victory in a field event at worlds or the Olympics.

"I'm sure, as we continue, we will have many Kenyans coming up in the field events and the sprints," Yego said. "We have talent there."

Other gold medalists included Cuba's Yarisley Silva in the pole vault and Zuzana Hejnova of the Czech Republic in the 400 hurdles.

Meanwhile, a few more U.S. medal hopefuls walked away empty-handed.

They included four-time national champion Emma Coburn in the steeplechase and two-time Olympic medalist Jenn Suhr in the pole vault. Suhr pulled her groin during warmups and couldn't clear 4.80 meters.

"There's more physio tape going around right now than I've seen," Suhr said of the U.S. training room. "It's been a hard world championships. It looks like people are tired."

Not among the fatigued was Gatlin. The American sprinter enjoyed another easy run in the 200-meter semifinals to set up another showdown with Bolt on Thursday night.

Gatlin ran his semifinal heat in 19.87, the second-fastest semifinal ever run at worlds.

Bolt ran his in 19.95, and was basically jogging to the finish when he turned to his left and saw South African sprinter Anaso Jobodwana making a funny face at him. The two shared a laugh.

"It's the third time I've been in a semifinal with him," said Jobodwana, who has now run next to Bolt in two world championships and the London Olympics. "I'd (always) been right next to him and kind of making him run, even though he really wasn't really running."

For Bolt and Gatlin, the real running comes in the final, when Bolt will try to extend his record by winning a 10th career gold medal at the world championships.

To open Thursday evening's festivities, van Niekerk will step to the top of the podium to receive his gold medal.

Nobody can say he didn't work for it.

"It's what the sport is all about," Merritt said. "You get to the championships, and you leave it all on the track."

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This story has been updated to correct the first name of Pieter Lourens.