The big goal for both sprinters remains the world championships in Beijing in August.
"Right now, I can't consider myself the favourite because it's months away," Gatlin said. "I'm just trying to stay healthy and strong. But having two world leads does put me in position to say entering a race, 'OK, I'm the man to go out there and go against.'"
Gatlin was in Rome preparing to run the 100 in the Golden Gala on Thursday.
Gatlin beat Bolt at the Stadio Olimpico two years ago, although the Jamaican is not entered this year.
Gatlin clocked 9.74 seconds in the Diamond League opener on May 15 in the sweltering heat of Doha, Qatar. Only four sprinters have ever run faster, including Bolt, who set the world record of 9.58 in 2009.
Gatlin won the 200 in 19.68 in Eugene, Oregon, last weekend, matching his personal best.
He will be aiming for his fourth career win in Rome, the fourth stop of the Diamond League.
"I'm just starting off where I left off last year," Gatlin said. "I want to go out there and dominate each race, and that's what I've been doing."
His opponents on Thursday include former European indoor champion Jimmy Vicaut, 2003 world champion Kim Collins, 4x100 world record holder Nesta Carter, and Mike Rodgers of the U.S.