The 2004 Olympic champion, who is returning to action after a four-year ban for failing a drugs test, clocked a time of 10.17 seconds — running into a headwind — to beat fellow-American Rubin Williams.
The 28-year-old Gatlin, who won two races at a meeting in Rakvere, Estonia, on Tuesday, is having to compete at smaller venues because he is still banned from some of the larger meetings.
“I am very glad with the result. My aim was to be better than at the last competition and I bettered that today by seven hundredths of a second,” he told the AFP news agency.
“I am dedicating myself fully to sport now and plan to return stronger next season,” Gatlin added.
Despite the run, Gatlin has admitted he still has some way to go before he can rival the likes of Usain Bolt, Tyson Gay and Asafa Powell once again.
“I am taking my return at the moment with a modest aim – the only aim I have in front of me is to be better than last time at every competition,” he said.
Gatlin will next compete in Joensuu, Finland on August 21 and has stated that he plans to return to Estonia for the indoor season.