Jessica Pegula saved a match point en route to a gritty 7-6 (7-2), 4-6, 7-5 win over Linda Noskova on Thursday to advance from her round-robin group at the WTA Finals and send fellow American Coco Gauff packing from the season-ending championships.

Pegula hit a career-high 16 aces while Wimbledon champion Noskova committed a career-high 15 double faults in a see-saw battle that lasted two hours and 45 minutes at the tournament, which was moved from Riyadh to Indian Wells because of the US-Israeli war on Iran.

"I've learned that sometimes the serve feels good and sometimes it doesn't, and how to manage the days when it doesn't and to ride it when you are serving well," Pegula told reporters.

"I don't think I served that well in my first couple matches and I served great today. Sometimes there's no rhyme or reason."

Noskova, Gauff and Pegula all finished 2-1 in the group, while alternate Marta Kostyuk went 0-3.

Noskova won the group with a 5-2 record in sets, followed by Pegula at 5-3 and Gauff at 4-3.

The win sets up a first meeting between Pegula and Russian teenager Mirra Andreeva in Saturday's semi-finals.

"It's the match people wanted, well now you are going to get it," Pegula said.

She had earlier called Andreeva "a diva" who "needs to be humbled", but did not realize her remarks were being livestreamed during a practice session before the tournament. In the same comments, Pegula also praised the world No 3, and she apologized afterward to those involved.

"She's fast, she has a great serve, she's strong, she hits the ball pretty hard and she's smart," Pegula said on Thursday.

"I'm going to do my best."

Gauff rallies past Kostyuk

Earlier, Gauff rallied to beat Kostyuk 6-4, 7-5 on a sun-soaked Stadium Two.

After sealing the first set with a stab volley that sent fans leaping to their feet under sunny California desert skies, Gauff rallied from 5-1 down in the second, winning six consecutive games.

"I was fully prepared to play a third set there," said Gauff, who needed treatment on her back during the second set.

"It's the last tournament of the season so I just wanted to finish it on a high note and give myself the best chance to play the semi-finals. Either way, I didn't want to be sad walking off the court."

Kostyuk, who won the Madrid title and reached the French Open semi-finals, was already eliminated before her match against Gauff after losing to Noskova and Pegula.

Kostyuk, who joined the eight-player tournament as an alternate after world No 1 Elena Rybakina withdrew because of illness, failed to win a set in her three matches as she struggled with a wrist injury.