BEIJING, March 3 -- China's Li Na has failed to advance in women's singles at the Qatar Open while two Chinese pairs have reached the women's doubles semi-finals.

    During the quarter-final match Thursday night, Li Na fought hard against world number eight Nadia Petrova of Russia. 

    She stayed strong after her serve had been broken by the powerful Russian rival in the first game, going head to head until the tenth game when she committed some errors to give up the first set 6-4.

    Li was obviously shaken by her mistakes and lost the first game again in the second set. However, she recovered to break Petrova's serve and even the score. But Petrova's serves finally proved too powerful, sealing the set at 6-4.

    It's Li Na's fourth loss against world top ten players in recent years, losing all matches with close scores.

    Earlier, in women's doubles quarter-finals, Australian Open champions Yan Zi and Zheng Jie and Athens Olympic champions Li Ting and Sun Tiantian have all defeated their rivals to reach the semi-finals.

    Second seeded Yan and Zheng have managed to score four out of nine break points to win the match 7-5, 6-3.

    Li and Sun beat their rivals 7-6, 6-4.