John Isner advanced to the BB&T Atlanta Open semi-finals after a 7-5 4-6 6-1 win over Mischa Zverev on Friday.

Isner, 33, dropped only two first-serve points in the match and hammered 21 aces past the German, and is now 29 wins and four losses in total at the event.

World-number-nine Isner has won four of the previous five tournaments at Atlantic Station and will play Matthew Ebden, who defeated the American in four sets at the Australian Open earlier this year, for a place in another decider.

"He is a tough player. I played well today, I needed to," Isner said after his win against Zverev.

"It was a weird match. The balls were bouncing everywhere and it was tough to control. I was happy to get through in three sets.

"I am definitely playing better than I was at the beginning of the year. I was struggling a little bit. To his credit, he played much better than me that day in Australia. Now, I’m playing in my backyard and he beat me in his backyard. We’ll see if I can turn the tide."

Ebden reached the semi-finals after requiring little more than an hour to beat Marcos Baghdatis 6-3 6-2.

The Australian is yet to drop a set in Atlanta, but will present a stern challenge against Wimbledon semi-finalist Isner, as he pursues a maiden ATP title.

In the other half of the draw, Nick Kyrgios trailed Brit Cameron Norrie 7-5 3-0 before retiring hurt in the evening match.

Norrie now faces American Ryan Harrison after he defeated Hyeon Chung 6-7 6-2 7-6 (7-5) to advance to the last four.