Aryna Sabalenka moved one step closer to winning her first title of the year, prevailing in a 1-6, 6-3, 6-2 comeback Thursday night over Sloane Stephens to reach the quarterfinals of the San Diego Open.

The No.3 seed Sabalenka stormed back from a first-set rout to win in a smidge over 2 hours and maintain her undefeated record against Stephens. Sabalenka is now 3-0 over 2017 US Open champion Stephens, with all of those wins going to a decisive third set.

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Sabalenka started the week as No.7 in the Race to the WTA Finals, and a deep run in San Diego could move her further up the ladder as she seeks a second consecutive appearance at the year-ending championship.

San Diego: Sabalenka maintains undefeated record vs. Stephens

In her first match since making her second straight US Open semifinal (following a first-round bye this week), Sabalenka hit 23 winners to Stephens' 15.

After splitting the first two sets, Sabalenka took charge in the third by slamming a return winner to break Stephens at love for 4-2. Sabalenka fell behind 0-40 in the next game, but she deployed aggressive shots, especially with her serve, to reel off five points in a row and consolidate for 5-2.

Sabalenka broke Stephens for the sixth time in the following game to wrap up the win, lining up a meeting with former Top 20 player Donna Vekic in the quarterfinals. Vekic, who qualified for the main draw this week, has beaten Sabalenka in four of their five meetings.

Also on Thursday night, two other players looking to qualify for the WTA Finals faced each other in the second round, and it was Madison Keys who reached the San Diego quarterfinals by taking down No.8 seed Daria Kasatkina 6-4, 6-3 and notching the 250th tour-level win of her career.

Keys, No.13 in the Race to the Finals coming into this week, battled back from 4-0 down in the opening set before clinching victory in 1 hour and 27 minutes. Kasatkina is No.6 in the Race to the Finals but will have to wait a bit longer before her fate is determined.

"I knew that today would be really difficult against Dasha, she’s obviously had a really great season so far and has played some really good tennis," Keys said. "I’m really glad I was able to get back in that first set and be able to ride that momentum."

Keys had a 7-0 lead in her head-to-head with Kasatkina at the start of the year, but Kasatkina finally got a win on the board in their rivalry in their lone previous match this season, at Melbourne Summer Set 2.

However, the pendulum swung back Keys' way Thursday, as she notched exactly 50 percent of points returning the Kasatkina first serve en route to the win.

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Keys will face her fellow American Jessica Pegula in the quarterfinals. It will be the first meeting on tour between Keys and No.4 seed Pegula.

In the nightcap match, No.2 seed Paula Badosa eased into the quarterfinals with a 6-0, 6-3 dismissal of qualifier Louisa Chirico. Badosa required only 53 minutes to eliminate World No.196 Chirico.

Video Highlights: Badosa's key plays in second-round win

Chirico is back in the Top 200 for the first time since 2017, and she earned her first tour-level main-draw win since that year by upsetting Alison Riske-Amritraj in the first round this week.

However, Badosa had already cruised past Chirico once this season, losing just three games in their sole previous meeting, in the first round of Wimbledon. Badosa dropped the same number of games Thursday, but she had to fight back from a break down twice in the second set.

Badosa started the week at No.12 in the Race to the WTA Finals, as she is in contention for her second straight showing at the year-end championship. Badosa will aim to keep her run going when she has her first meeting with Danielle Collins in Friday's quarterfinals.