As a high school freshman in Greensboro, N.C., weighing his prospects for a basketball career, John Isner was forced to admit that dribbling was not his specialty.

“I couldn’t handle the ball at all,” Isner said. “Not even average.”

That has changed dramatically in adulthood: Isner is a standout dribbler in an entirely different sport. His penchant for bouncing the ball between his legs as he plants his left foot and squares up to the baseline is a key component of the buildup to his serve — one of the biggest ever.

Isner used his pet basketball move, virtually without fail, to usher himself into position on the 91 serves he uncorked in his straight-sets, first-round victory over Guillermo García-López at the United States Open on Tuesday. It’s not exactly reminiscent of the fancy dribbling that Kyrie Irving will soon bring to the Nets, but the basketball-style bouncing gives Isner’s service routine a hint of flash.

“Now it looks like I know what I’m doing,” Isner, 34, said. “But the ball is tiny — and there’s a lot of space there.”