Usain Bolt slowed coming around the bend, looked to his left and saw his lead shrinking.
So the Jamaican turned the speed back up a notch for a few strides, enough to ensure he would win his semifinal heat in 20.18 seconds Wednesday night, moving closer to becoming the first man with two Olympic golds in the 200 meters.
The man two lanes over who was gaining on Bolt, Anaso Jobodwana of South Africa, finished in 20.27 to reach Thursday's final.
Bolt already successfully defended his 100 title from Beijing on Sunday.
The 200 final will include Bolt's teammate and training partner, 100 silver medalist Yohan Blake, who won the first heat in 20.01. Wallace Spearmon of the U.S. was second in 20.02, with Christophe Lemaitre of France next in 20.03 to also advance.
Churandy Martina of the Netherlands, Warren Weir of Jamaica and Alex Quinonez of Ecuador round out the field.