WASHINGTON (Reuters) - Three times champion Andy Roddick won the 500th match of his professional career with a hard fought 7-6 6-4 third round victory over fellow American Sam Querrey at the Washington Classic on Thursday.

Roddick is the 36th player overall and fourth active to achieve the milestone, along with Roger Federer (657), Carlos Moya (573) and Lleyton Hewitt (511), with the win putting him in the quarter-finals of an event he last won in 2007.

"It's a pretty small number of players who have gotten there, an elite group," Roddick told reporters. "I've done it with enough time to add to it.

"It is validation of consistency in my career."

Hewitt, meanwhile, failed to add to his tally, dropping a 4-6 6-3 7-6 decision to second seed and defending champion Juan Martin del Potro of Argentina.

Tenth seed Tommy Haas defeated Juan Carlos Ferrero 7-5 2-6 6-1, while Robin Soderling, the fifth-seed, managed to edge Marc Gicquel 7-5 5-7 6-3.

Fourth seeded Fernando Gonzalez had an easier time, stopping American Wayne Odesnik 6-2 6-4, while number 11 Ivo Karlovic defeated qualifier Somdev Devvarman 7-5 6-1 to set up a clash against Roddick.

Roddick, playing in his first tournament since his epic five-set final loss to Federer at Wimbledon, struggled with his serve at times. He did manage three aces but also committed six double faults and dropped his serve twice.

"I served badly tonight but it's gratifying because it was a match I wouldn't have won a few years ago," Roddick said. "I didn't know what the outcome would be.

"He is game-ready and I was coming off the bench."

By contrast, Querrey felt there was nothing wrong with Roddick's serve.

"He was serving just so well," Querrey said. "The most impressive thing is his serve percentage... it is one thing to hit it 135 miles an hour, but to get 65 to 70 percent in is incredible."

(Writing by Roger Lajoie in Toronto; Editing by John O'Brien)