John Isner’s latest match wasn’t the smoothest of his week in Atlanta, but the top-ranked American did enough to draw one step closer to his ultimate goal.

Isner defeated Reilly Opelka 6-7(5), 6-4, 6-2 in the semifinals of the Atlanta Open on Saturday night. The No. 1 seed found himself in a tight contest but eventually prevailed thanks to missed opportunities from Opelka and Isner’s overpowering serve.

“It was a tough match,” Isner said. “I knew any given set could come down to a few points here or there. That’s what happened in the first set. I broke him pretty early in the second set, and that definitely settled me down.”

Opelka’s first set victory came on a rare miscue by Isner. Up 5-3 in the set’s tiebreaker, Isner delivered a rare double-fault to keep Opelka alive. The 18-year-old obliged and promptly won three of the next four points to take the set.

“His serve was too good,” Opelka said. “I won (the first set), but I was lucky, to be honest.”

With rumblings of an upset lingering, Isner eased such thoughts in the second set. He quickly won four of the first five games thanks to his serve as well as errors made by Opelka in several rallies. Isner took the final game to force the match-deciding third set.

Isner said his confidence remained high after the gaffe in the first set, which showed with his play in the second.

“It wasn’t like I was playing poorly,” Isner said. “I had to keep holding serve and putting pressure on him because I was definitely closer on his service games than he was on mine.”

Isner entered the third set having won all 11 games in which he served. His dominance in the service game remained just as strong when it mattered.

Isner and Opelka traded game victories through the first four games, but Opelka’s chances diminished with the fifth game. After forcing Isner to deuce, Opelka saw Isner take the advantage. With Isner’s dominance when serving apparent, Opelka knew he needed to force another deuce to stay alive.

Instead, he double-faulted, which gave Isner a 3-2 lead.

“The double fault was huge,” Isner said. “I felt like there were some nerves and tension in that moment.”

From there, Isner was in control. He won the next three games to come out victorious.

Isner advances to the finals and plays No. 2 seed Nick Kygrios on Saturday. He credited Kyrgrios for being one of the sport’s next stars and said this year’s final may be the toughest he’s ever faced.

With his fourth consecutive Atlanta Open title now in reach, Isner said winning the tournament yet again would be a special achievement.

“Even when I became an established pro, I never could imagine winning the same tournament four times, let alone four times in a row,” Isner said. “Regardless of the outcome tomorrow, making the finals of this tournament six of the seven years is not too shabby.”