Tokyo, Japan (My Sportsbook) - Playing his first match since winning the U.S. Open last month, top-seeded Argentine star Juan Martin del Potro was stunned by French qualifier Edouard Roger-Vasselin, 6-4, 6-4, in first-round action at the $1.226 million Japan Open.

Del Potro, last year's Tokyo runner-up to Czech Tomas Berdych, lost to a player who was participating in only his third main-draw match (1-2) of 2009. The 25-year-old Roger-Vasselin, who is currently ranked 189th in the world, hadn't won at ATP-level match since July of last year.

It was last month when del Potro captured the biggest title of his career by dethroning Roger Federer in five sets at the U.S. Open, snapping the super Swiss' 40-match winning streak at the tournament. Yet, on Tuesday, del Potro couldn't solve Roger-Vasselin, who saved all six break points he faced.

Meanwhile, third-seeded Frenchman Gilles Simon stayed hot with a 6-3, 6-4 handling of Japanese wild card Takao Suzuki, a fifth-seeded and reigning Tokyo champion Berdych blasted Japanese wild card Go Soeda 6-2, 6-4, and eighth- seeded Lleyton Hewitt topped Japanese wild card Tatsuma Ito 6-1, 7-5. Simon is fresh off his title in Bangkok last week. The former world No. 1 Hewitt captured this Tokyo event back in 2001.

In other Day-2 action, Austrian Jurgen Melzer bested Argentine Leonardo Mayer 7-6 (7-4), 6-3 and 36-year-old Frenchman Fabrice Santoro outlasted Kazakhstan's Andrey Golubev 6-7 (5-7), 7-6 (7-2), 6-2 at Ariake Colosseum.

The 2009 Tokyo champ will claim $300,000.