WTA roundup: Marta Kostyuk tops 1 seed Jessica Pegula in San Diego

Marta Kostyuk of Ukraine stormed back in the first set and won a tense tiebreaker, and then cruised to a semifinal victory over top-seeded Jessica Pegula of the U.S. at the Cymbiotika San Diego Open on Saturday night.

With the 7-6 (4), 6-1 victory, Kostyuk, the sixth seed, will take on Katie Boulter of Great Britain in Sunday's final. Boulter, ranked 49th in the world, crushed the third seed, Emma Navarro of the U.S., 6-3, 6-1.

Kostyuk trailed Pegula 5-1 in the first set before winning five straight games, including twice breaking the top seed on serve. Pegula regrouped to tie the match at 6-6.

Kostyuk, who came from behind to defeat fourth-seeded Anastasia Pavlyuchenkova of Russia in a quarterfinal match on Friday, then broke away from a 3-3 tie in the tiebreaker. She won the set on her second set point.

Boulter won 88 percent of her first-serve points, to 62 percent for Navarro. She also dominated by winning 67 percent of return points on second serve.

ATX Open

Sixth-seeded Xiyu Wang of China clinched a two-set victory in a tiebreaker to defeat the top seed, Anhelina Kalinina of Ukraine, 6-3, 7-6 (4), in Austin, Texas.

Wang's opponent in Sunday's final will be countrywoman Yue Yuan, the eighth seed. She dispatched Anna Karolina Schmiedlova of the Slovak Republic 6-0, 6-3.

Wang broke away from a 3-3 tie to win the first set over Kalinina, but they battled throughout the second set, with each player losing her serve twice en route to the 6-6 tie.

Kalinina led the tiebreaker 3-2, but Wang won three straight points, including on Kalinina's serve for a 5-3 edge. Kalinina won the next point, but Wang won the next two points on serve to take the match.