Usain Bolt took the initial, loping steps towards securing the first Olympic sprint double since Carl Lewis in 1984 when he cruised through his first-round 200 metres heat on Monday.
Jamaica's Bolt claimed the 100 metres gold with a spectacular world record on Saturday but has said all along that the 200, in which he was a world championship runner-up last year, is the race closest to his heart.
In Monday's heats he caught Nicaragua's Juan Zeledon within about four strides before going on to ease home in 20.64 seconds, just behind Trinidad's Sorillo Rondell.
Defending champion Shawn Crawford and this year's 100 metres bronze medallist Walter Dix also went through comfortably. Wallace Spearmon completed the U.S. trio progressing.
The second round takes place later today with the semi-finals on Tuesday and final on Wednesday.