By Mark Lamport-Stokes PACIFIC PALISADES, California, Feb 16 (Reuters) - Former shoe salesman James Hahn knows as well as anyone how difficult is to win on the PGA Tour, and will always be thankful that his hard work finally paid off at last year's Northern Trust Open. Aged 33, the American journeyman clinched his maiden PGA Tour title in a three-way playoff with compatriot Dustin Johnson and England's Paul Casey and now, 12 months later, he is excited to be back at Riviera Country Club as the defending champion. "Getting the first victory on Tour really solidified that what I'm doing is the right thing at this point in my life," Hahn told reporters at Riviera Country Club on Tuesday while preparing for Thursday's opening round. More...