All eight second-round matches were played Thursday to make up for time lost due to rain earlier in the week.
Isner had a battle on his hands before downing Jack Sock 7-5, 6-7 (3-7), 7-6 (7-3) in a match that took 2 ½ hours.
Ricardis Berankis earned a chance against Isner in the quarterfinals with a 6-3, 6-3 upset over second-seeded Tommy Haas.
In other second-round matches, Ruben Ramirez Hidalgo ousted No. 6 seed Fernando Verdasco 6-3, 6-2, Rhyne Williams fought past Ivo Karlovic 6-4, 6-7 (5-7), 7-6 (7-3), Juan Monaco eliminated Tim Smyczek 7-6 (7-5), 6-1 and qualifier Robby Ginepri defeated Martin Alund 6-2, 4-6, 6-4.
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