Reilly Opelka fired 39 aces and held on through the longest tiebreaker in ATP Tour history to beat John Isner 7-6 (9/7), 7-6 (24/22) Saturday to reach the final of the Dallas Open.
The decisive 46-point tiebreaker in the second set was the longest in a tour-level match since the start of the ATP Tour in 1990.
Opelka, the second seed, finally put it away on his eighth match point when he slid a backhand winner past Isner to end one of the rare rallies in the servers' duel.
It came after a run of 26 straight points on serve.
"I lost track," Opelka said when asked to describe the tie-break, referring to the unprecedented seven changes of end. "At one point it was 21-all. That's something I've never seen before, but if it was going to happen, it certainly would have been in this match.
"It just shows how clutch he is," he said of Isner. "I had some house money being up a set. He didn't, and he hit some unbelievable spots on his serve down match point."
Opelka will now face Jenson Brooksby who outlasted Marcos Giron in a three-set encounter, 6-4, 6-7 (4/7), 7-6 (7/5) in the other all-American semi-final.
Brooksby was better on the pressure points across the almost three-hour match. He won despite hitting fewer aces (three to seven) and serving more double faults (two to none), winning just 68 percent of his first-serve points compared to 75 percent for Giron.
"Brooksby is one of my favorite players to watch, probably my least favorite player to play," Opelka said.
Third-seeded Isner fired a relatively modest 21 aces, but like Opelka he never faced a break point.
Isner had 10 set points in the second-set tiebreaker. His best chance came on his own serve at 9/8, but Opelka managed to beat him at the net.
Opelka has now claimed nine of a dozen consecutive tiebreakers he has played against Isner, pushing his record against his compatriot to 4-1 -- the only loss coming in their first meeting in Atlanta in 2016.
Isner was also involved in the longest tennis match of all time, a five-set marathon win over Frenchman Nicolas Mahut at Wimbledon in 2010 that spanned three days and lasted over 11 hours.Â
Opelka will be seeking a third career title.
This year's Dallas Open was the first time four Americans have featured in the semi-finals of an ATP tournament since San Jose in 2004, when Andy Roddick won the tournament.