Fellow American Paul Drayton took silver; it was the fifth time in six Games that the United States had the top two finishers.
Edwin Roberts gave Trinidad and Tobago its first medal in the men's 200 metres with his bronze.
Two of the six finalists from the 1960 Games returned: gold medalist Livio Berruti of Italy and fourth-place finisher Marian Foik of Poland.
The United States made its 14th appearance, the only nation to have competed at each edition of the 200 metres to date.
The "fastest loser" system introduced in 1960 was not used, with the number of heats in each round make it unnecessary.
He ran the same time in the final, but Henry Carr won in 20.3 seconds to set a new Olympic record.