Usain Bolt completed the first leg of his ‘triple treble’ quest with victory in the 100 metres at the Rio Olympics.
Bolt, 29, ran 9.81 seconds in his final Olympics to replicate his success at Beijing 2008 and London 2012.
Gatlin, twice banned for doping offences, finished 0.08 seconds behind Bolt to take silver.
“Somebody said I can become immortal. Two more medals to go and I can sign off. Immortal,” said Bolt.
“It wasn’t perfect today but I got it done and I’m pretty proud of what I’ve achieved – nobody else has done it or even attempted it.
“I expected to go faster, but I’m happy that I won. I did what I had to.”
The Jamaican, who is targeting further success in the 200m and 4x100m relay, eventually got up to speed and overhauled Justin Gatlin to win his seventh Olympic gold in 9.81 seconds.
Bolt, who wrapped up the Olympic sprint treble in Beijing and London, has signalled his intentions to retire after the 2017 World Championships in London.
“I’m really happy,” Bolt told BBC Sport. “I expected to go faster, but I’m just happy I won.”
Bolt was slower out of the blocks than 34-year-old Gatlin, who was aiming to regain the title he won at Athens 2004.
But he surged through from 60 metres to pass Gatlin and comfortably win his seventh Olympic gold.
Bolt received a hero’s reception as he walked out into Rio’s Olympic Stadium before the race, and the crowd chanted his name after his victory.