In the title match Sunday, Mauresmo will face sixth-seeded Russian Vera Zvonareva, who defeated seventh-seeded countrywoman Nadia Petrova 6-3, 7-6.

The third-seeded Sharapova was scheduled to face France's Mauresmo in a night semi-final. But she withdrew earlier Saturday citing a right shoulder strain.

Sharapova suffered the injury in Zurich two weeks ago, then aggravated it in her quarterfinal victory over Alicia Molik on Friday.

"I'm very disappointed I am not able to continue my play in Philadelphia," the Russian said. "I was having a really good tournament and I'm sure it will still be an exciting final weekend. I just wish I could be a part of it."

Mauresmo said: "I would have liked to play her. But the day was over earlier than I thought."

Mauresmo, ranked number one in the world earlier this year, will be seeking her fifth WTA Tour singles title of the year and the 15th of her career.

Zvonareva, 20, will be in search of her second crown of 2004 and the third singles triumph in her career.

Already with her performance this week, Zvonareva has booked her berth in the season-ending WTA Tour Championships next week.

"Qualifying (for the Champion-ships) took a lot of the pressure off today," Zvonareva said. "It's great to beat a Top 10 player."

After winning the first set against Petrova, Zvonareva surrendered a 5-3 lead in the second and had to fight through a tiebreaker.

"I was keeping my concentration but then I lost it and relaxed and waited for her errors," said Zvonareva, who raced to a 5-1 lead in the tiebreaker.

This week started with two berths in the elite event up for grabs, which have been claimed by Zvonareva and Serena Williams, who didn't play in Philadelphia.

Mauresmo has won all four of the lifetime meetings with Zvonareva.

"Tomorrow, I think the physical is what will be most important," Mauresmo said. "And I believe I am better."