John Isner continued winning tiebreakers and forced another tie after the match.
The two-time defending champion won the battle of the tallest players on the ATP tour, defeating Ivo Karlovic of Croatia 7-6 (3), 7-6 (3) on Friday to advance to the semifinals of the Hall of Fame Tennis Championships.
In the other quarterfinal match, No. 4 seed Lleyton Hewitt of Australia beat qualifier Jan Hernych of the Czech Republic 6-7 (3), 6-4, 6-2, setting up a rematch of last year's final when Isner captured the title in straight sets.
On Friday, Isner won his 13th straight match on Newport's grass courts and raised his mark to 13-0 in tiebreakers during the streak.
When it was over, Isner, listed at 6-foot-9, claimed his height is listed incorrectly by the ATP short an inch, which would tie him with Karlovic as the tallest player ever on the tour.
"I'm 6-10," he said, drawing attention from an ATP media official assigned to the event. "That was like my college height. No one from the ATP busted out the measuring tape. They found it online or something."
He was then asked by a writer: "Do you want to be listed at 6-10?"
"Yeah, because that's what I am," he said. "I'm not trying to hide that. I was probably still growing in college."
The second-seeded Isner served 23 aces, including three in each of the tiebreaks. Karlovic had 14 aces, but double faulted on the match's final point.
Both players served over 70 percent in the match, most ranging between 120-130 mph. Neither broke in a game.
"He served at a pretty high percentage," said Isner, ranked 19th in the world, the highest American coming into the week. "Anytime guys like us serve in the 70's, it's going to be tough for anyone to break us."
The 1 hour, 37 minute match, played in humid conditions with peeks of sunshine, had few extended points.
"When I'm able to inch ahead in tiebreakers it gives a lot of confidence, especially when I know the match is on my serve at that point," Isner said.
Karlovic played his first ATP tournament since being sidelined with spinal meningitis from late April to early May. He called for trainer early in the opening set, moving his arms from side to side, explaining what was wrong while sitting in his chair.
"I was dizzy a little bit and it was difficult to focus," the 34-year old said. "I was a little worried that it was the virus or something. It wasn't. I was tired. I wasn't used to playing that many matches."
Karlovic, ranked 167 coming into the week, was satisfied with how he played in the tournament.
"I was just happy I was here," he said. "If anyone told me I'd be in the quarters, I would say he's nuts."
Isner closed out the first tiebreaker with an ace.