The American regained his eligibility to compete in July but he was expected to have difficulty finding races even after the ban ended because of a Euro Meetings recommendation not to invite athletes who bring disrepute to the sport.
He won the 100m and 200m sprint double at the 2005 World Championships to add to his 2004 Olympic 100m title but has been out of action since June 2006, although he still hopes to race at the 2012 Olympics.
Gatlin got off to a sluggish start on Sunday, but his acceleration at the halfway point helped him to pull away from the rest of the field and finish the race comfortably in first place.
"I think it was a good race," said Gatlin. "My body's been aching a bit due to a lot of training."
Gatlin is next likely to race at the Joensuu Games in Finland on 21 August.
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