Bolt stumbled out of the blocks in heat four but was soon into his running and looking around at his competitors - the Jamaican doing just enough to win in 10.09.
But that time looked positively pedestrian after first Justin Gatlin and then fellow American Ryan Bailey broke 10 seconds for the first time in the heats of the Olympic Games.
Gatlin clocked 9.97 in heat two, only for Bailey to then equal his personal best of 9.88 in the next heat to raise hopes that Bolt's world record of 9.58s could be under threat in tomorrow's semi-finals and final.
Bolt's oft-stated hopes of becoming a 'legend' of the sport by defending his 100m and 200m titles had looked in doubt after he lost twice to compatriot Yohan Blake at the Jamaican Trials and needed treatment on a stiff back which was causing hamstring problems.
The 25-year-old insisted last week he was fit and ready to compete against the likes of training partner and world 100m champion Blake, who eased to victory in 10.00 in his heat.
Bolt said: 'I am feeling good, my legs are feeling good so I am happy. I am training well so I feel like I'm back. My start was good, I am only focused on the semi-finals.'