Atlanta - Three-time defending champion John Isner beat Taylor Fritz 7-5, 6-4 on Friday night in an all-American match to advance to the Atlanta Open semi-finals.
The 6-foot-10 Isner set up a match with the man who replaced him as the tallest American player on the ATP World Tour, 6-foot-11 American teen Reilly Opelka.
"He's had a great run," the top-seeded Isner said about Opelka. "I'm certainly going to try to end it, but it's going to be very tough."
Isner overpowered Fritz, the 18-year-old seeded eighth, with 20 aces for his 14th straight victory in the hardcourt event. The former University of Georgia star has reached the finals five of the previous six years.
"It was a good win," Isner said. "The first set was obviously tight. I was feeling good and feeling strong. In the second set, I had to keep holding serve as well as I could, and I did that."
The 18-year-old Opelka topped seventh-seeded Donald Young 6-4, 6-4 in another all-American match to reach his first tour semi-final.
"I've been doing a really good job with my movement, winning points on my opponent's serve," Opelka said." ''The way I am serving now, I know I can at least get to a tie-break. But being able to hit good returns and passing shots is huge."
In the other semi-final, second-seeded Nick Kyrgios of Australia will face Japan's Yoshihito Nishioka.
Kyrgios beat fifth-seeded Fernando Verdasco of Spain 6-4, 6-7 (5/7), 6-3, and Nishioka topped Argentina's Horacio Zeballos 6-4, 6-4 to reach his first tour semi-final.
"I've been working on my serve a lot. More percentage, more power," the 20-year-old Nishioka said. "And before I was very emotional, throwing rackets and getting frustrated. But I've been more calm since Wimbledon. I think that's why I'm winning more now."
Kyrgios won in Marseille, France, in February for his lone tour title.