HOUSTON — Tall, big-hitting Americans John Isner and Reilly Opelka joke about being “serve-bots” and their similar styles of play will be on display against each other in the final of the U.S. Men’s Clay Court Championship.

The fourth-seeded Isner, who won the Houston title in 2013, hit 17 aces Saturday to eliminate reigning champion Cristian Garin 4-6, 6-3, 6-4 in the semifinals. The third-seeded Opelka had 21 aces while beating Nick Kyrgios 6-3, 7-5.

The final Sunday will be the sixth career meeting between the 24-year-old Opelka, who is listed by the ATP at 6-foot-11, and the 36-year-old Isner, who is listed at 6-10.

Opelka leads 4-1 head-to-head, with four victories in a row.

“When guys like Reilly and I lock horns,” Isner said, “it’s going to be tiebreakers.”

Talk about an understatement.

The last 12 sets they contested all went to tiebreakers, including one Isner called “ridiculous” on Saturday. That’s because it went to 24-22 in the semifinals at Dallas in February – the longest tiebreaker in an ATP match since 1990. Opelka landed 39 aces in that win, 18 more than Isner.

Isner is up to 71 aces this week after playing three consecutive three-set matches, breaking his own Houston record of 64 aces for the tournament, which he established in 2013.

“Clay is a good surface for guys like Reilly and I,” Isner said. “Our serve is good anywhere. In my opinion, we don’t need a fast court to hold serve. And both of us maybe prefer a little bit of a slower court, to get into points and give ourselves time to wind up for shots. Faster courts make that a lot tougher.”

He is into his first tour-level clay final since Houston nine years ago and first final on any surface since on Atlanta’s hard courts in August 2021.

Opelka, meanwhile, got to his third ATP final of this season; only 21-time Grand Slam champion Rafael Nadal has more, four.

This is the first tour-level final on a surface other than hard courts for Opelka, who is ranked 18th in the world.