A relaxed Coleman, who also posted the fastest time in the opening round, looked imperious as he eased up 10 metres from the finish then coasted across the line for a comfortable win.
The time was just off of Coleman's season best of 9.81 ran in June and confirmed his status as the gold medal favourite heading into the final later on Saturday.
It was not such smooth sailing for the 37-year-old Gatlin.
With the top two from each of three semi-finals advancing directly, Gatlin needed one of the two fastest remaining times to book his spot.
Canadian Andre De Grasse, a triple Olympic medallist at the 2016 Rio Games returning to form after a string of injuries, won the heat in 10.07 ahead of Jamaican 2011 world champion Yohan Blake, leaving third-place finisher Gatlin waiting to see if his 10.09 would see him through.
Gatlin's spot was confirmed after South Africa's Akani Simbine took the final heat in 10.01 ahead of Britain's Zharnel Hughes with the remainder of the field unable to better the American's time.