RIYADH, Saudi Arabia — The thing that separates Aryna Sabalenka from all the other players on the Hologic WTA Tour is her ability to conjure magic on command. It’s a pretty good trick.

Down repeatedly in the first set to Coco Gauff, Sabalenka willed her way out of trouble Thursday and went on to a 7-6 (5), 6-2 victory to book her semifinal berth at the WTA Finals.

On Friday, the No. 1-seeded Sabalenka (3-0) will take on No. 4 Amanda Anisimova (2-1), while No. 5 Jessica Pegula (2-1) meets No. 6 Elena Rybakina (3-0). Earlier, Pegula was a 6-2, 6-3 winner over Jasmine Paolini.

While the first set was effectively a dead heat, Sabalenka wrested control in the second. In the end, she converted five of six break points. Gauff was 3-for-7 and finished with six double faults.

Sabalenka came into the match with a commanding (but not clinching) record of 2-0 in round-robin play. When Pegula won the night’s first match over Jasmine Paolini, it meant that the 1-1 Gauff could eliminate her by winning in straight sets and advance herself.

The two hadn’t met since their entertaining final at Roland Garros, in which Gauff lost a first-set tiebreak, then came back to win in three. Sabalenka admitted she lost her composure and vowed to do better, and she did, winning the US Open.

Heading into the match, there were a number of possible scenarios that allowed Sabalenka, Pegula and Gauff to advance. When Gauff got the early upper hand, it looked like — with a straight-sets victory — she might eliminate the World No. 1.

The 21-year-old American broke Sabalenka to open the match before a good crowd at the King Saud University Indoor Arena. Serving at 2-all, Sabalenka survived two more break points with some big serving.

Gauff was serving for the first set at 5-4 when doubt crept into her game. On break point, she stroked an ill-advised drop shot that Sabalenka easily retrieved and sent down the line for a forehand winner. 

The tiebreak was all Gauff early, as she took a 3-1 lead, causing Sabalenka to drop her racquet in disgust. It was 4-2 when the tide turned. Gauff might have won the set if she’d landed a backhand at net, but it found the net. Sabalenka came back with two impeccable serves, and it was 5-4.

“I was thinking, `OK, there is nothing to lose,’ she said. “And I was going big on my serves. It really helped me to find my rhythm. After that game I was serving much better. Yeah, that was a great decision to go big and try to find the rhythm.”

It was back on serve when Gauff made the fatal mistake. Double faults have dogged her recently; she had 17 in her opening match here. But there were only three in her second match and, to this point against Sabalenka, her slate was clean. The double gave Sabalenka a 6-4 lead and she converted her second set point with a gorgeous plus-one, finishing it off with a forehand winner.

“I was already working for the second set, to be honest,” Sabalenka said. “Something clicked and I was able to break and that game gave me a lot of confidence that I still got it in this set. And yeah, super happy to get this win.”

The second set was not particularly competitive until Gauff scored a break in the sixth game. Sabalenka broke right back and locked it down, at love, and finished with another strong service game.

“I had a lot of chances in the first set,” Gauff said. “It was a bit disappointing not to get that one. She stepped her level up and I just couldn’t find it after that. Overall, I think I was playing a high level.

“Couple points in the tiebreaker, I had literally on my racket. Yeah, it was a tough one.”

Sabalenka showed her customary grit and gusto — and maybe a little something extra. This is her fifth consecutive trip to the year-end championships and she has yet to win a title. Her best effort is a runner-up finish three years ago to Caroline Garcia.