Zheng Saisai of China celebrates with the winner's trophy after defeating Aryna Sabalenka of Belarus in San Jose, California on Sunday. Photo: VCG

Zheng Saisai knocked off her fourth-seeded opponent to capture her first career WTA title with a straight-set win over Aryna Sabalenka in the final of the San Jose WTA  tournament on Sunday.

The unseeded Zheng, who also beat Sabalenka in their only other career meeting, used a solid serving performance to beat the second seed from Belarus 6-3, 7-6 (7/3).

"I don't have so much ­experience because it is the first time for me," a nervous Zheng said on the court during her ­trophy presentation speech. 

"I am very excited about how I played the whole week.

Zheng said the San Jose tournament had special meaning for her even before she won on Sunday.

"Five years ago I got my first WTA singles win here and now I win my first WTA title here," she said.

Zheng clinched the victory in the second-set tiebreaker when Sabalenka doubled-faulted on the first championship point.

The top seed also double-faulted to get to championship point as she finished with eight double faults compared to just five for Zheng.

After the 25-year-old Zheng downed eighth-seeded American Danielle Collins, she beat fourth-seeded US teen Amanda Anisimova in a three-set quarterfinal marathon. In the semis, Zheng ousted No.7 seed Maria Sakkari in straight sets. 

Zheng, who was not broken in the one-hour, 45-minute match, won 72 percent of her first-serve points compared to 52 percent for Sabalenka.

"She played great tennis," Sabalenka said of Zheng.

Sabalenka, 21, was playing in her first final since winning the Shenzhen Open in China in January.

She lost in the first round of qualifying at this event last year but then went on a run that saw her shoot from 36th in the world to her current No.10 ranking.