AFP - American Justin Gatlin roared to a 100m victory in Japan on Sunday, as track and field's pantomime villain kicked off his preparations for this summer's Rio Olympics.

Floored by Jamaican sprint king Usain Bolt in the 100m and 200m at last year's world championships, two-time doping offender Gatlin clocked a time of 10.02 seconds into a slight head-wind in Kawasaki in his first test of the season.

"Definitely it's given me motivation, but also it's made me smarter and wiser," Gatlin said of his Beijing disappointment.

"Usually you can come with a strategy that can combat the whole field," added the 34-year-old after finishing well clear of Japan's Ryota Yamagata (10.21) and Ramon Gittens of Barbados (10.26), despite a sore right ankle.

"But when you go against someone like Usain, who is unique in stature and talent, you've got to come with a contingency plan, a plan B."

Gatlin had been unbeaten in 28 races over two years before Bolt's ruthless Beijing take-down of his American rival, whose frustration at being demonised in the media was plain to see.

"It has made me a smarter and wiser competitor to know when to stay within my technique, execute my race and just worry about myself," said Gatlin, who runs in Shanghai next week.

"I rolled my ankle in November - it was almost a break. It's still swollen so to be able to come out here and run this race, just smooth, I'm happy with that."