Nick Kyrgios beat John Isner in straight sets at the Atlanta Open on Sunday to end the American's three-year grip on the title.
Top seed Isner had won each of the last three instalments of the ATP World Tour 250 event but went down 7-6 (7-3) 7-6 (7-4) to the second seed.
Isner put early pressure on Kyrgios with three break points in the Australian's first service game, but that was the closest either player came to sealing a break.
The 21-year-old, whose only other professional title came earlier this year in Marseille, held his nerve in stifling temperatures to take the first tie-break 7-3.
Isner had another break point at 5-5 in the second set but Kyrgios' serve held up and he again won the tie-break to win his second title of 2016.
"I want to thank John," Kyrgios said after the match. "He's one of my best friends on tour. I don't have too many right now."