"I just tried to put the ball inside. Nothing more," the Frenchman said. "I don't know why I lost the second set and won the third set 6-love."
Isner won just 5-of-27 of Haas' first serves and 5-of-26 second serves.
"My second serve was very good today," Haas said. "I used that to move him around a bit.
"I was glad to get a break early. You want to try to get a good start, because once he gets up in breaks and gets relaxed with his serve, he's tough."
Third-seeded Dmitry Tursunov of Russia, the defending champion, advanced to the quarterfinal round when his opponent, American
Wayne Odesnik, withdrew with a back injury before the night's final match.