Donna Vekic maintained control of her rivalry with Aryna Sabalenka via a hard-fought quarterfinal triumph at the San Diego Open on Friday. She will face No.19 Danielle Collins in the semifinals on Saturday.

Former Top 20 player Vekic defeated No.3 seed Sabalenka 6-4, 6-7(5), 6-1 in 2 hours and 37 minutes to reach her first semifinal of the year. Vekic improves her head-to-head lead over Sabalenka to a commanding 5-1.

World No.77 Vekic had to come through qualifying this week, and she has been in top form once she hit the main draw. Vekic has beaten three Top 25 players in succession, with wins over Maria Sakkari and Karolina Pliskova preceding her victory over Sabalenka.

San Diego: Vekic's top points from her quarterfinal win over Sabalenka

2022 San Diego

Despite the loss, Sabalenka is still in the hunt for one of the five remaining singles spots at the WTA Finals in Fort Worth. Sabalenka started the week at No.7 in the Race to the Finals, as she aims for a second straight appearance at the prestigious year-ending event.

Read more: Pegula to pull double duty at the WTA Finals

Vekic won nearly three-quarters of her first-service points as she held on for another win over Sabalenka. By beating World No.5 Sabalenka, Vekic notches the tenth Top 10 win of her career, with her ninth Top 10 win coming against Sakkari in the first round.

Vekic was two points away from a straight-set win, but Sabalenka came back from 5-4 down in the second-set tiebreak to push the match into a decider. However, Vekic regrouped in the third set, where she converted two of her three break points while saving the lone break point she faced.

Vekic will face Collins for a spot in her first WTA 500 final since 2019 St. Petersburg. Collins advanced to her second semifinal of the season without losing a set all week, defeating No.2 seed Paula Badosa 7-6(5), 6-4 to notch her fourth Top 10 win of the season.

Against Badosa, Collins jumped out to a 4-1 in the first set before thwarting a furious comeback from the Spaniard. Both players squandered their chance to serve out the set before Collins edged Badosa 7-5 in the tiebreak. 

Collins took a medical timeout during the set break but kept her focus early in the second set. Serving at 2-3, the American surged ahead, winning 14 of the next 18 points to earn a chance to serve out the win. Collins saved two break points in the final game before finding the line-painting accuracy that boosted her into the Australian Open final in January.

"I think today is just an example of no matter how well you're playing, no one is immune to having bad days," Collins said. "I was definitely working through some things on court and it was really challenging at times, especially playing against Paula. She doesn't give you a lot of free points and was making me work for everything."

Collins leads the head-to-head 1-0 against Vekic and is bidding to make her first final since Melbourne. Collins is remains in the hunt for a qualifying spot at the WTA Finals, having come into San Diego at No.17 on the Race Leaderboard.

"It's great seeing Donna back healthy and playing really good tennis," Collins said. "She has a big game and a lot of weapons. I'm just going to have to try my best."