NEW HAVEN, Conn. (AP) -- Top-ranked Caroline Wozniacki still had her father coaching her Thursday as she remained undefeated at Yale, advancing to the semifinals of the New Haven Open with a 7-5, 6-3 win over 19-year-old American Christina McHale.
Wozniacki is 15-0 at the WTA's final tuneup before the U.S. Open and is the tournament's three-time defending champion.
Last week, after losing to McHale in Cincinnati, Wozniacki said she would be changing coaches. But Piotr Wozniacki was back by her side when she called for a coach during the first set on Thursday.
"Well, you know, I don't want to talk too much about it because the other coach I've been working with, he doesn't want to have his name out. I have to respect that,'' she said. "But my dad is still there. He's still my coach at these tournaments, still going to be out and coaching me and being my support. But I'm getting some help from the sideline as well.''
After getting some advice from dad, Wozniacki broke McHale to win a close first set, and again in the eighth game of the second set.
McHale was the only American in the draw and was playing just the second quarterfinal of her young career. She said Wozniacki seemed more aggressive than she was a week ago."She was pushing me around the court more this time,'' she said. "I think I could have served better today.''
Wozniacki's semifinal opponent will be third-seeded Francesca Schiavone, who advanced when Anabel Medina Garrigues withdrew due to a knee injury.
Second-seed Li Na endured several hours of rain delays and three sets of tennis before advancing in her quarterfinal, 6-4, 3-6, 6-2, over Russia's Anastasia Pavlyuchenkova. Li will play Czech qualifier Petra Cetkovska who beat fourth-seed Marion Bartoli 7-5, 7-5.
Li's match was supposed to be played at 1 p.m., but didn't start until after 3:30 p.m. and was stopped for more than two hours after the first set because of rain at the Connecticut Tennis Center.
When it finally resumed, Pavlyuchenkova grabbed the momentum, winning four games in a row to go up 4-2, and eventually take the set.
The French Open champion broke the Russian to go up 1-0 in the third, and finished off the match after Pavlyuchenkova twisted her right ankle in the second game of the set and needed a medical timeout.
"I think today is the longest match I ever played,'' Li said. "I think I was warmed up a hundred times already. Like because after the rain stop, you have to warm up again.''
Cetkovska won in another rain-delayed match on the grandstand court. She was down 5-4 in each set before rallying to break Bartoli in the 11th game of each and serving out the win.
"I was trying to be even more concentrated because at these moments, always the end of the sets, these moments are the key moments,'' she said. "I tried to do the best, tried not to miss anything, not to give any single point.''
Medina Garrigues of Spain withdrew a day after injuring her right knee during a win over Elena Vesnina of Russia.
She said the decision to withdraw was precautionary and she expects to play in next week's U.S. Open.
"It's not so bad,'' she said. "But, it's very uncomfortable because it's painful for the situation.''