Coco Vandeweghe upends Vera Zvonareva in La Costa tennis

Reporting from Carlsbad — The La Costa Resort on Thursday resembled a high school graduation, where families cheer for their own despite warnings not to do so.

The graduate in this case was Coco Vandeweghe, an 18-year-old just a year removed from high school, making it big for the first time as she took the world’s No. 9 player to a third set -- and won.

Vandeweghe threw her fist, not her visor, in the air after hitting the winning shot in her 2-6, 7-5, 6-4 victory over Vera Zvonareva in the second round of the Mercury Insurance Open. The normally silent tennis crowd had been shouting encouragement throughout the match and stood to cheer the Rancho Santa Fe resident, a qualifier making her deepest run ever through a WTA tournament.

“I love playing in front of a big crowd, especially it helps when they’re behind you,” Vandeweghe said.

A rout looked imminent after Zvonareva took the first game, but Vandeweghe wouldn’t be beaten so easily.

“She decided to be a little bit more aggressive,” said an emotional Zvonareva, the tournament’s No. 3-seeded player and this year’s Wimbledon runner-up.

The next challenge for Vandeweghe, ranked No. 200 in the world but assuredly rising fast, will be a nationally televised quarterfinal bout against veteran Svetlana Kuznetsova. The young player admitted to nerves before her match against Zvonareva, but may still be riding high by Friday afternoon’s match.

“It was pretty cool,” Vandeweghe said. “That’s not a great word but it’s the best one I can come up with right now.”

Following No. 1-seeded Jelena Jankovic’s shocking loss to Alisa Kleybanova on Wednesday, it was clear no one was safe as the second round concluded in Carlsbad.

After No. 4-seeded Flavia Pennetta opened the day with a 6-4 first-set victory, Maria Kirilenko fought back to a 4-1 lead in the second set. But Pennetta took the next four games and eventually won the set and match in a 7-5 tiebreaker.

Pennetta will face No. 2-seeded Samantha Stosur in Friday’s quarterfinals, which begin at noon. Pennetta defeated Stosur for the Los Angeles Open title a year ago.

“It’s going to be a really good match,” Pennetta said. Stosur “is one of the best players right now. I think she’s in good shape.… It’s going to be really tough.”

Kuznetsova defeated Sara Errani, 6-1, in the first set of what looked like a quick second-round match, and led at the break in the second set. But Errani fought back to win the set in a tiebreaker, 7-6 (7-5), and stayed close in the third set, which Kuznetsova won, 7-5.

“I need matches like this,” Kusnetsova said. “This is positive because I won and I fought. It was really hard to fight.”

Daniela Hantuchova was the only singles player to have an easy day as she beat Jie Zheng, 6-2, 6-1. Hantuchova upset No. 6-seeded Marion Bartoli in the first round of the tournament.

Zheng and Kirilenko’s day wasn’t all bad, though, as the No. 4-seeded pair advanced to the semifinals in the doubles draw with a 6-3, 6-0 win over Urszula Radwanska and Chanelle Scheepers. They will face the doubles team of Zvonareva and Kusnetsova.

laura.myers@latimes.com