SAN DIEGO (AP)Top-ranked Iga Swiatek overcame a challenge from qualifier Donna Vekic on Sunday to win the San Diego Open title 6-3, 3-6, 6-0.

Swiatek earned her tour-leading 64th victory of the season heading into the WTA Finals that begin Friday in Fort Worth, Texas. The event features the tour’s top eight singles and doubles teams.

The 21-year-old won her eighth title of the season, including the French Open and U.S. Open earlier this year.

”I’ve worked hard with my coach and my psychologist to keep focused on those moments that make it easier to close the match,” Swiatek said. ”I just wanted to be proactive in making my shots.”

Speaking in her native Polish, Swiatek thanked the vocal Polish contingent that exhorted her with chants of ”Iga! Iga!”

”I wanted to be the one who hit the last ball in, use my patience more and not think too much,” said Swiatek, who ascended to world No. 1 some seven months ago following the surprise retirement of Australia’s Ash Barty.

Swiatek was awarded a winner’s check of $116,340 along with a yellow surfboard.

Americans Coco Gauff and Jessica Pegula won the doubles final, defeating Gabriela Dabrowski of Canada and Giuliana Olmos of Mexico 1-6, 7-5, (10-4). Top-seeded Gauff and Pegula had to play two full matches on Sunday because rain postponed the semifinal match.

After Vekic won the second set, Swiatek left no doubt about her dominance in the final set with her array of topspin cross-court forehands and looping shots that flustered her tiring opponent.

”I managed to win the second set, but in the third I just hit the Iga wall,” said Vekic, who came into the first-year WTA event as an unseeded qualifier, winning seven matches in eight days.

”She played out of this world,” the Croatian added. ”She showed why she’s definitely the best player in the world right now.”

An unlikely finalist, Vekic, ranked 77th, reached the finals only a few hours before her match with Swiatek, claiming a 6-4, 4-6, 7-6 (2) semifinal win over unseeded Danielle Collins of the U.S.

Spread over two days due to Saturday night’s two lengthy rain delays, the Vekic-Collins match totaled three hours, including Sunday’s 32-minute finish. Collins re-started with a 4-2 edge in the third set, but Vekic battled back to earn the finals berth.

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