The No. 4-ranked Ruud lifted his career record to 9-0 at Geneva, where he won back-to-back titles in the past two years. The clay-court event is a final warmup for the French Open. Ruud was runner-up there last year.
Ruud double-faulted on his first match-point chance against the 49th-ranked American before taking the second with a forehand winner as he advanced to the net.
"It's a great win for me. J.J. is an aggressive, tough player," said Ruud, who will face Nicolas Jarry in the quarterfinals Thursday.
Jarry advanced when his opponent, sixth-seeded Tallon Griekspoor, withdrew ahead of their match.
Fourth-seeded Grigor Dimitrov, who got a wild card into the Geneva draw, eased past Roberto Carballes Baena 6-1, 6-4 to earn a quarterfinals match against 85th-ranked Christopher O'Connell of Australia.
O'Connell led 6-0, 3-0 against Bernabe Zapata Miralles when the seventh-seeded Spanish player retired from the match.