The Rio Olympic silver medallist started slowly but rallied to dip ahead of Asuka Cambridge, who finished .03 seconds behind the American, while another Japanese, Shuhei Tada, came third in 10.35.
Any hopes of clocking a fast time were scuppered by a 1.2-metre headwind at the Todoroki Stadium, although Gatlin said he was pleased with his performance in testing conditions.
“It was a tough wind, but the competition was even tougher going against some of the future stars of Japan,” the 35-year-old was quoted as saying by Kyodo. “They put together a good race, and they’re going to be formidable opponents.
“I’ve been a little bit injured, not being able to train as hard as I want to, but I’ve been working on my finish and it helped out today.”
Canada’s Aaron Brown won the men’s 200m in a time of 20.62, while Bulgaria’s Ivet Lalova-Collio doubled up to claim the women’s 100 and 200m.
(Writing by Simon Jennings in Bengaluru; Editing by John O’Brien)