WARSAW, Poland - A day after the No.2 seed went out, the No.1 seed followed suit. Caroline Wozniacki saw her Polsat Warsaw Open dreams come to an end on Thursday, losing the first set of her quarterfinal match against Zheng Jie before retiring due to a right ankle injury.

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Wozniacki, who had actually lost two of her three previous meetings with Zheng, got broken in the sixth game of the match and couldn't recover, losing a lengthy 56-minute set, 6-3, then retiring.  Highlights: Zheng vs. Wozniacki

"I sprained my ankle in Charleston and it has been bothering me since then," Wozniacki said. "I felt some pain from the beginning of the match today. I spoke to the physio and she said it would only get worse. I'm really sad. I wanted to win this match. I wanted to win the whole tournament. But health is the most important thing, and I didn't want to risk having a worse injury."

"I knew she had a problem with her ankle yesterday. My coach told me I should forget about it, though, and just concentrate on myself," Zheng said. "I feel lucky to make the semifinals here, but I wish we could have finished our match today."

Wozniacki wasn't sure she would be ready for Roland Garros: "I have to talk to the doctor and see what we can do with this injury. My ankle was taped really well today and I still felt some pain, so I don't know. I hope I can play."

Zheng missed the second half of 2007 with an injured left ankle, but rebounded to have an amazing 2008, highlighted by a semifinal run at Wimbledon.

"I injured my ankle on clay, so when I'm on this surface I'm always very careful and a bit nervous about it," Zheng said. "I'm more confident with each match."

Check out some of Zheng's best moments in this special gallery!

Next for the No.5-seeded Zheng is qualifier Greta Arn, who upset No.6 seed Alona Bondarenko in a marathon three-setter, 57 64 64. Bondarenko was a runner-up here last year but couldn't get past the tricky Arn, who mixed big serves in with a variety of spins and pace to outlast the Ukrainian No.1.

Earlier in the day, Li Na - at No.3 now the highest seed remaining in the Premier-level tournament - breezed past Sara Errani, 62 61. They just played in Stuttgart a few weeks ago, Li prevailing, 61 61.  Highlights: Li vs. Errani

"I just played her in Stuttgart, but my coach told me this morning the court here is very different from there," Li said about her win over the feisty Italian. "I just had to concentrate on every point and I did that. I played consistently."

After becoming China's first Top 10 player earlier this year, Li had somewhat of a slump, including a four-match losing streak between Dubai and Miami - but she has found her feet again on clay courts, reaching the quarters at Stuttgart and Madrid and the semis here. She is one of the form players going into Paris.

"After Miami I went back to my home and took a 10 day break - 10 days without tennis," Li said. "After that I felt ready for tennis again. I went to Munich and started training very hard. I'm glad to see the hard work has paid off so far."

Next for Li is the defending champion, Alexandra Dulgheru, who rallied from 3-5 in the second set to send qualifier Tsvetana Pironkova home in straight sets, 64 75.  Highlights: Dulgheru vs. Pironkova