The 16-year-old lived up to his billing as the pre-race favourite as he charged to victory in 20.
“I took the win from the Jamaicans. I took the win from everybody else. I definitely wanted to prove that we’re (U.S.) still on top,” he said.
“Coming in with a big target on your back, there’s always pressure. But you can’t worry about it, you’ve just got to run your own race and do the best you can.”
Jamaica did win the women’s 200m final when Natalliah Whyte scored in 23.55 seconds on the busiest day of the Games, with 33 gold medals decided, including 12 in athletics.
Anatoly Ryapolov won the men’s long jump with a distance of 7.54m while Kenya’s Gilbert Kwemoi Soet won the men’s 1,500m, and celebrated by performing a series of karate kicks.
Gabriel Luis Moreno made it the archery field just in time to join forces with China’s Li Jiaman and win the mixed international team event.
Moreno almost missed his event after his taxi driver got lost but got there in the nick of time.
“I had to go into the quarter-finals with almost no warm up time,” he said. “But thankfully, that did not harm my performance.”
Britain’s Giarnni Regini-Moran and Nikita Nagornyy of Russia each won their third gold medals in men’s gymnastics in Nanjing.
Regini-Moran, who won the all-around and floor golds earlier in the Games, won the vault while Nagornyy added the parallel bars to his earlier wins in the pommel horse and rings.
China’s Wang Yan picked up her second gold when she won the balance beam while Brazil’s Flavia Lopes Saraiva and Japan’s Kenya Yuasa both struck their first golds.
China’s Yang Hao won the men’s three-metre springboard diving final, sealing the victory with a forward two-and-a-half somersault.
Alexandr Lifanov of Russia took the gold in the men’s modern pentathlon individual event.
Singapore claimed two golds on the water when 15-year-old Samantha Yom and Cheok Khoon Bernie Chin won their sailing events.
Argentina’s Francisco Cruz Saubidet Birkner won the men’s windsurfing gold on a countback from Russia’s Maxim Tokarev while China’s Wu Linli dominated the women’s event.
China’s Xu Shilin won the women’s tennis singles gold, beating Iryna Shymanovich, who won the doubles on Saturday, 6-3 6-1, while Orlando Moraes Luz made amends for his loss in the men’s singles final when he teamed up with his fellow Brazilian Marcelo Zormann Silva to win the doubles.
New Zealand’s Emily Fraser managed to break Europe’s domination of the equestrian events when she won gold after a jump-off.
“It was nerve-racking,” Fraser said. “My horse was jumping during the warm-up before the jump-off, and I was hoping everything would go right.”
The Czech Republic beat Italy by the smallest of margins to win the international mixed relay, the last cycling event of the Games.
Belarus won two of the four gold medals on offer in canoeing and kayaking sprints with Kamila Bobr taking the women’s C1 and Stanislau Daineka winning the men’s K1.
Serghei Tarnovschi of Moldova won the men’s C1 while Russia’s Inna Nikitina was the winner of the women’s K1.
(Reporting by Julian Linden in Singapore; editing by Martyn Herman)