Top seed John Isner fired 15 aces in a 7-6 (7/2), 6-2 victory over Japan's Go Soeda on Thursday to reach the quarter-finals of the ATP Delray Beach International Championships.
The American player broke Soeda twice in the 75-minute match to book a meeting with defending champion Kevin Anderson of South Africa.
Anderson, seeded sixth, continued his comeback from elbow surgery with a 6-4, 3-6, 6-3 victory over Taiwan's Lu Yen-Hsun.
German second seed Tommy Haas also advanced to the quarters of the $455,775 tournament, but US third seed Sam Querrey was eliminated.
Haas ousted Uzbek Denis Istomin 6-4, 6-1, moving on in 67 minutes without facing a break point, while Latvian qualifier Ernests Gulbis outlasted Querrey 6-4, 4-6, 7-6 (7/4).
Next for Haas will be a Friday quarter-final against Croatian Ivan Dodig, who downed Russia's Evgeny Donskoy 6-3, 7-5.
Gulbis will face fellow qualifier Daniel Munoz, a Spaniard who outlasted Belgium's Xavier Malisse 7-6 (7/3), 3-6, 6-3 to reach the last eight in a match that was halted Wednesday in the first set by rain.
The persistent showers meant no matches were finished Wednesday, leaving all of the second round to be completed Thursday.
Lithuanian lucky loser Ricardas Berankis advanced, rallying to defeat American Jack Sock 3-6, 6-4, 6-1. His next foe is France's Edouard Roger-Vasselin, who eliminated Croatian Ivo Karlovic 6-4, 7-5.