Roddick defeated Nicolas Mahut 7-6 (7-4), 6-3 in the rain-delayed match. Mahut, who had downed Roddick in the opening round of this year's French Open, served 14 aces.
Roddick bounced back from a struggling start to the season to win a Wimbledon tune-up last month. He has captured at least one tournament in 12 straight years -- the first of his titles coming in Atlanta in 2001.
Michael Russell will face Roddick in the quarterfinals after downing fifth-seeded Kevin Anderson 6-7 (5-7), 6-4, 6-4.