Roddick cracks his 500th win with Washington victory

The three-time champion, top-seeded at this edition, holds 27 career titles and, with Thursday's victory, improved to 27-4 in Washington. He was only the fourth active player to reach 500 wins - joining Roger Federer, Carlos Moya and Lleyton Hewitt.

Querrey came to Washington with the Los Angeles title in hand after playing two finals in proceeding weeks in Newport and Indianapolis.

"Sam's in form, having won in LA," said world number five Roddick. "He had a month of good matches behind him. It was a tough win."

Defending champion Juan Del Potro of Argentina advanced into the last eight over 2004 winner Hewitt 4-6, 6-3, 7-6 (7-2) as the Australian, 28, prepares for the US Open starting in just more than three weeks.

Fourth-seeded Fernando Gonzalez put out American Wayne Odesnik 6-2, 6-4 while French Open finalist Robin Soderling of Sweden, seeded fifth, stopped Frenchman Marc Gicquel 7-5, 5-7, 6-3.

Czech eighth seed Tomas Berdych eliminated German Philipp Petzschner 4-6, 6-3, 6-3.

German 10th seed Tommy Haas won a battle of veterans against Spain's Juan Carlos Ferrero 7-5, 2-6, 6-1 while 11th seed Ivo Karlovic of Croatia advanced against Indian qualifier Somdev Devvarman 7-5, 6-1.