John Isner wowed with a career-high first-serve percentage of 92 on Friday. (AP)

UNIONDALE, N.Y.—When a big man thumps an ace at the New York Open, the resulting sound is a thwack—the thwack of the ball hitting the wooden back wall, which is covered by just a thin layer of black material.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

A post shared by New York Open (@nyopentennis) on

Watch a lot of the New York Open, and you'll hear that sound relentlessly as Sam Querrey (6'6"), John Isner (6'10") and Reilly Opelka (6'11") have all served their way into Saturday's semifinals.

"Tall guys united!" Querrey exclaimed following his three-set quarterfinal win over Jason Jung, in which he hit 23 aces in less than 90 minutes. "I always cheer for the guys over 6'6". Especially, having a tournament in America, I want as many Americans to do well as possible."

Reilly Opelka, who dispatched Guillermo Garcia-Lopez, 6-3, 6-4, while winning 83 percent of his first-serve points, said he shares Querrey's support for the Americans, though they don't have to to be tall.

"I root for Frances [Tiafoe] and [Taylor] Fritz,” he said, which makes sense considering the 21-year-old is almost a decade younger than Querrey.

And John Isner, who defeated Jordan Thompson, 6-4, 6-2, in his quarterfinal, expressed a similar sentiment, saying, “We’re all really good friends—not just the tall ones—all of us Americans in general."

Isner made a career record 92 percent of his first serves on Friday, and won 78 percent of those points.

What makes the temporary courts at the Nassau Coliseum such a server's paradise, players say, is the combination of the controlled indoor environment and the fast bounce of the black surface. The only obvious difficulty for the tall guys here is getting a good strike on the balls that skid low. 

"Look at the finals last year," Opelka pointed out. "Querrey and [Kevin] Anderson, two guys that both serve really well."

The Isner-Querrey-Opelka trio is joined in the semifinals by Canadian Brayden Schnur, who's come through qualifying and won five total matches so far this week, despite having  never previously recorded an ATP win. 

Schnur will face Querrey in the first singles semifinal on Saturday. They'll be followed by an Australian Open rematch between Isner and Opelka, who both have a career service holding rate of 90 percent or higher.

Thwack.