Svetlana Kuznetsova shows young Coco Vandeweghe how it’s done at La Costa

Reporting from Carlsbad — 

Sporting bright pink shoes and a blond ponytail, Coco Vandeweghe made 25-year-old Svetlana Kuznetsova look positively old on the tennis court Friday afternoon.

But experience proved to be an advantage for Kuznetsova.

Vandeweghe, an 18-year-old from Rancho Santa Fe putting together an improbable run at the Mercury Insurance Open in Carlsbad, held a 5-2 lead in the first set of her quarterfinal against Kuznetsova. But the unseeded Russian had learned enough about Vandeweghe’s game to use it against her, and took the next five games on her way to a 7-5, 6-2 victory.

“It’s hard when you go on the court and you have no clue how the other girl is going to play,” said Kuznetsova, who has won two Grand Slam singles titles. “. . . The first game was like, wow, she hits the ball great. But I said, ‘OK, I have to fight, I have to be very consistent and let’s see what she’s made of.’ ”

Reaching the final eight was the farthest Vandeweghe, a qualifier, had advanced in a WTA tournament. She defeated No. 3-seeded Vera Zvonareva on Thursday, and had the semifinals in sight before Kuznetsova’s comeback.

“You win that first set, you only have one more set to go and it’s a different match,” Vandeweghe said. “But things happen for a reason, I think, and I’m happy with the way I’ve played. I won all those matches in a row, and I’ve beaten great players along the way.”

After playing six matches in seven days in Carlsbad, Vandeweghe will have a few days off before beginning main-draw play at Cincinnati on Monday or Tuesday. She earned a wild-card spot into the draw.

“I keep hearing from my coach [and] some other people that this is a great breakthrough tournament for me,” Vandeweghe said.

Kuznetsova, who won the U.S. Open in 2004 and the French Open in 2009, will face No. 5-seeded Flavia Pennetta in the afternoon semifinal on Saturday. Pennetta defeated No. 2-seeded Samantha Stosur, 6-4, 6-3, in Friday’s first match.

It will be Kuznetsova’s first semifinal singles appearance in 2010.

“It’s going to be a really tough match, I think,” Pennetta said. “She’s not in good shape but she can be very dangerous. When she plays good, she can beat everyone.”

No. 4-seeded Agnieszka Radwanska will face Daniela Hantuchova in Saturday’s evening semifinal.

Hantuchova defeated Alisa Kleybanova, 2-6, 6-4, 6-3. She lost the first set and trailed, 3-0, in the second set before taking charge of the match.

“It was a matter of getting her tired,” Hantuchova said.

Radwanska took two quick sets from No. 7-seeded Shahar Peer in a 6-2, 6-0 victory in Friday night’s featured match.

Only four seeded players survived to the quarterfinals at La Costa Resort, and Pennetta and Radwanska are the only two to reach the semifinals.

“It’s not easy,” Pennetta said. “It’s never easy to beat this kind of player.”

laura.myers@latimes.com