Top-seeded Caroline Wozniacki of Denmark retired with an injured ankle while trailing China's Zheng Jie 6-3 on Thursday in the quarter-finals of the Warsaw Open. Zheng's compatriot, third-seeded Li Na also advanced to the semi-finals after beating Sara Errani of Italy 6-2, 6-1.

Li Na and Sara Errani of Italy met in Stuttgart recently and Li won that encounter 6-1 6-1.

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. After taking the first set 6-2, Li quickly cruised to a 5-1 lead in the second. She then reached the quarters after Errani returned the ball wide. She is one of the form players going into Paris.

"I prepared very well for today's match. I had an easy win against her in our last matchup in Stuttgart. But, my coach reminded me that the court here is quite different and also asked me to play with all my efforts in the match. And, I played with my rhythem today." Li said.

Next up for Li is defending champion Alexandra Dulgheru of Romania who beat Bulgarian qualifier Tsvetana Pironkova 6-4 7-5. Meanwhile, Caroline Wozniacki saw her Warsaw Open hopes come to an end. She lost the first set of her quarterfinal match against Zheng Jie before retiring due to a right ankle injury.

Wozniacki, who had lost two of her three previous meetings with Zheng, got broken in the sixth game of the match and couldn't recover. She lost a lengthy 56-minute set, 6-3, then calling it quits in the pair's fourth meeting.

Next for the fifth seed Zheng is Greta Arn of Hungary.