Top-ranked Caroline Wozniacki was expecting a challenge at the Family Circle Cup — and she got it from a 48th-ranked player from the Czech Republic.

The top-seeded Dane had to win two tiebreakers to defeat Barbora Zahlavova Strycova 7-6 (6), 7-6 (9) in a stadium court match that lasted more than 2½ hours. It looked nothing like the 56-minute cakewalk Wozniacki enjoyed in Wednesday's opening match.

"I knew that it wasn't going to be easy. I've seen her before and played her last year here," Wozniacki said.

Wozniacki appeared to be cruising again with a 4-1 lead in the opening set against Zahlavova Strycova. Then the frustrated Czech talked to her coach and promised to play more aggressively. The move worked: She extended points and forced Wozniacki deep into corners to chase down shots.

Zahlavova Strycova held serve twice to force the tiebreaker. The 25-year-old fought back in that one, too. After trailing 5-1, she won five straight points to hold a set point of her own. But Zahlavova Strycova sent that chance long and netted the next two points to give Wozniacki the set.

It was Wozniacki's turn to rally in the second set after Zahlavova Strycova took a 2-0 lead. She twice held serve with Zahlavova Strycova ahead to force a second tiebreaker, thrilling the fans at the Family Circle Tennis Center.

Wozniacki moved in front 5-2, but Zahlavova Strycova fought off four match points. Zahlovova Strycova had a chance to take the set leading 9-8 but sent the ball wide.

Moments later, she put up a defensive lob on a hard hit ball into the deep right corner and Wozniacki pounded it up into the grandstand.

Zahlavova Strycova said she was proud of her performance.

"Against these players, you have to risk a lot and you have to be aggressive," she said.

Wozniacki will play the sixth seed, Yanina Wickmayer of Belgium, for a spot in the semifinals.

Wozniacki reached the finals two years ago before losing to Sabine Lisicki. She retired with an ankle injury in the semifinals last year.

"Every time I go into a tournament, I'm trying to win it," she said. "That's my focus."

Wozniacki said she's counting on more difficult matches ahead in the clay-court season.

"This is the first tournament on clay," she said. "You need to get used to the conditions, you need to get used to sliding. There will be longer rallies in clay, there's no doubt about it, and the matches will most likely be longer."

Wozniacki is among three of the top 10 players competing here. Fifth-ranked Samantha Stosur, the second seed and defending champion, fell to Elena Vesnina 6-4, 6-1.

"Anytime you lose early in a tournament, it's not a good feeling," she said. "But especially in a tournament like this where I really enjoyed playing."

No. 8 Jelena Jankovic defeated Chanelle Scheepers 6-2, 6-2 in the night match. Jankovic will next face Christina McHale, an 18-year-old who is the youngest player among the world's top 100 at No. 97.

McHale, the last American in the singles draw, defeated Daniela Hantuchova 7-6 (3), 6-1.

Shahar Peer, ranked 11th, missed out on the chance to become the first Israeli woman ranked in the top 10 when she lost to Julia Goerges of Germany, 6-2, 6-3.