Eight-time Olympic champion Usain Bolt described his performance as "very bad" as he won his 100m heat at the World Championships in 10.07 seconds.
The Jamaican, who is retiring after the event in London, beat Great Britain's James Dasaolu into second (10.13) but was frustrated with his start.
"I'm not fond of these blocks," said Bolt. "I have to get this together."
The USA's Justin Gatlin, twice suspended for doping, was booed when he came out to race but eased through.
Britons Reece Prescod (10.03) and Chijindu Ujah (10.07) took top-three spots to reach Saturday's semi-finals.
Watch heat here