Bolt wanted to lower his world record of 19.19 seconds but the light drizzle at Olympic Stadium contributed to a slightly slower winning time of 19.78 in the final. After he crossed the finish line he slapped his leg.
Andre de Grasse of Canada took silver in 20.02 to go with his bronze in the 100. Christophe Lemaitre of France was third in 20.12, holding off Adam Gemili of Britain in a photo finish.
Bolt has eight Olympic gold medals and has the chance for a ninth as part of Jamaica’s 4×100-meter relay on Friday, when he’s aiming to complete a triple-triple of golds at the Summer Games.
Earlier, American Ashton Eaton defended his Olympic decathlon title, equaling the games record with a surge on the last lap of the 1,500 meters — the last event in the two-day competition.
The 28-year-old American finished with 8,893 points to match the Olympic mark set by Roman Sebrle of the Czech Republic in 2004.
Kevin Mayer of France was 59 points behind to take silver and Damian Warner of Canada took bronze with 8,666 points.