Argentine Juan Martin Del Potro upset top seed Andy Roddick 3-6, 7-5, 7-6 to win the Washington Classic on Sunday. Del Potro, 20, won the final-set tiebreak 8-6 to wrap up the two and a half hours contest.

The defeat was a blow to the fifth-ranked Roddick who would have enjoyed an otherwise perfect return to the tour after a month-long hiatus nursing his hip injury.

Juan Martin Del Potro of Argentina celebrates his win over Andy Roddick of the US in the finals of the Legg Mason Tennis Classic in Washington, August 9, 2009

Roddick's last play was in the Wimbledon final last month when the American lost to Roger Federer. The 26-year-old Roddick, however, said he was pleased with his effort, especially with the U.S. Open on the horizon.

"I'm not far off from where I was toward the end of Wimbledon," he said. "Coming in after being off for a month you want to fine out where your form is at."

Andy Roddick (L) of the U.S. talks to Juan Martin Del Potro (R) of Argentina after receiving their trophies following Del Potro's win in their finals match of the Legg Mason Tennis Classic in Washington August 9, 2009