Caroline Wozniacki of Denmark returns a shot during the women's quarterfinal against Agnieszka Radwanska of Poland at the Qatar Open tennis tournament in Doha, capital of Qatar, Feb. 15, 2013. Wozniacki lost 0-2. (Xinhua/Chen Shaojin)

China's Zheng Jie (L) and Spain's Nuria Llagostera Vives talk during the women's doubles quarterfinal against Germany's Anna-Lena Groenefeld/Czech Republic's Kveta Peschke at the Qatar Open tennis tournament in Doha, capital of Qatar, Feb. 15, 2013. China's Zheng Jie/Spain's Nuria Llagostera Vives lost 0-2. (Xinhua/Chen Shaojin)

Caroline Wozniacki of Denmark returns a shot during the women's quarterfinal against Agnieszka Radwanska of Poland at the Qatar Open tennis tournament in Doha, capital of Qatar, Feb. 15, 2013. Wozniacki lost 0-2. (Xinhua/Chen Shaojin)

Agnieszka Radwanska of Poland returns a shot during the women's quarterfinal against Caroline Wozniacki of Denmark at the Qatar Open tennis tournament in Doha, capital of Qatar, Feb. 15, 2013. Radwanska won 2-0. (Xinhua/Chen Shaojin)

Petra Kvitova of the Czech Republic reacts after losing a point during the women's quarterfinal against Serena Williams of the United States at the Qatar Open tennis tournament in Doha, capital of Qatar, Feb. 15, 2013. Kvitova lost 1-2. (Xinhua/Chen Shaojin)

Caroline Wozniacki of Denmark serves during the women's quarterfinal against Agnieszka Radwanska of Poland at the Qatar Open tennis tournament in Doha, capital of Qatar, Feb. 15, 2013. Wozniacki lost 0-2. (Xinhua/Chen Shaojin)

Agnieszka Radwanska of Poland returns a shot during the women's quarterfinal against Caroline Wozniacki of Denmark at the Qatar Open tennis tournament in Doha, capital of Qatar, Feb. 15, 2013. Radwanska won 2-0. (Xinhua/Chen Shaojin)