"I always feel comfortable playing here", Kyrgios said.
Just a day after the Australian told reporters if he's playing his best it would be "tough to lose", Kyrgios had to call it quits after reportedly suffering a hip injury.
John Isner joined elite company when he saved four of five break points en route to beating compatriot Ryan Harrison 5-7 6-3 6-4 to win the Atlanta Open for the fifth time on Sunday. "But we'll see what happens". Harrison beat Cameron Norrie of Britain 3-6, 6-3, 6-2 in the night match.
Seeking his fifth victory at Atlantic Station in the last six years, Isner will face eighth-seeded Ryan Harrison in a rematch of Isner's victory in the final last year. "That's how our sport goes sometimes, and I was very fortunate today".
He has 14 ATP Tour titles, breaking through for his first ATP Masters 1000 success at the Miami Open in April.
Isner ended runner-up in Atlanta in 2010 and 2011 before he lost in the semi-final in 2012.
The 23-year-old also landed himself in hot water during the Queen's Club Championships last month, when he was captured on live television simulating a sex act during a change of ends. He is also the only one in the group to ever win a tournament on the Tour - a pair of titles at Hamburg, including a year ago.
Kyrgios had looked in good shape in Atlanta a US Open series event that acts as a lead-up to the season's fourth grand slam, the US Open which starts on August 27 at Flushing Meadows.
Nicolas Jarry of Chile beat top-seeded Dominic Thiem of Austria 7-6 (5), 7-6 (7); Argentina's Leonardo Mayer topped second-seeded countryman Diego Schwartzman 6-3, 4-6, 6-3; and Georgian Nikoloz Basilashvili took down third-seeded Pablo Carreno Busta of Spain 7-6 (3), 6-4.
Kyrgios then doubled-faulted to give his British opponent the early break in the second, before the Aussie pulled the pin after 52 minutes, down 7-5 3-0.