Two-time defending champion John Isner and last year’s runner-up Lleyton Hewitt booked a semi-final showdown at the ATP Hall of Fame Tennis Championships on Friday.

Isner defeated Croatian Ivo Karlovic in a match in which the two towering players combined for 37 aces.

America’s Isner fired 23 of those en route to a 7-6 7-6 victory on the grass courts at the International Tennis Hall of Fame.

“I said the other day that this match would come down to a few points here and there, and those few points were in the tiebreak,” Isner said of a contest in which neither player dropped serve.

“I felt like I got a lot of good returns back and he came up with some good volleys. I made some good shots when I needed to,” Isner said.

Isner next faces Hewitt, the Aussie veteran out to avenge his defeat in last year’s final.

Hewitt, the fourth seed, defeated Czech qualifier Jan Hernych 6-7 6-4 6-2 in exactly two hours.

Hewitt has won three of four career encounters with Isner, including an upset at the Indian Wells hardcourt Masters in March.

In Saturday’s other semi-final, 35-year-old American Michael Russell will face 2007 Newport runner-up Nicolas Mahut of France.

Russell will be trying to reach his first career ATP final.