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BEIJING, Jan. 11 -- China's Li Na defeated Slovenia's Katarina Srebotnik in the Sydney International yesterday to book a place in the last four.

The 21st-ranked Li wore down Srebotnik in her quarterfinal, winning 7-5, 6-1 in 77 minutes, serving at a high 77 percent.

Li will face world No. 5 Kim Clijsters today. Clijsters swept into the semifinals after a quickfire victory over Israeli Shahar Peer. She took just 54 minutes to claim a 6-2, 6-1 victory over the 18th-ranked Peer.

Top-seeded Amelie Mauresmo was upset in the quarterfinals and Nikolay Davydenko, seeded No. 2 in the men's draw, became the fifth high-profile player to retire from the Australian Open warmup tournament.

Mauresmo, who won the Australian Open last year for her breakthrough Grand Slam singles title, lost 7-5, 6-0 to Serbia's Jelena Jankovic.

She had replaced No. 1-ranked Justine Henin-Hardenne as the top-seeded player in Sydney after the Belgian withdrew from this year's Australian events for undisclosed personal reasons.

Davydenko lost the first set 6-4 to Paul-Henri Mathieu of France before he retired due to pain in his right foot. He said he would travel to Melbourne for medical tests and assess his condition before next week's Australian Open.