Venus Williams and Jennifer Capriati's hopes of qualifying for next week's lucrative season finale were crushed by quarter-final defeats at the Advanta Championships in Philadelphia on Friday.
Sixth seed Vera Zvonareva of Russia pounded American Capriati 6-0, 6-1 to keep alive her chances of securing one of the two remaining places in the eight-player field for the $3 million WTA Tour Championships in Los Angeles which begin on Monday.
Top seed and defending champion Amelie Mauresmo of France helped Zvonareva's cause by toppling Williams 7-5, 5-7 6-1.
Venus holds a slight lead over Zvonareva in the points race but the two players trail Serena Williams, who is not competing in Philadelphia.
In other quarter-final action, seventh seed Nadia Petrova of Russia upset second-seeded compatriot and French Open champion Anastasia Myskina 6-3, 4-6, 6-4 to stay on course for her first career title.
Wimbledon champion Maria Sharapova also reached the last four after rallying to beat Australian Alicia Molik 3-6, 6-1, 6-3.
Mauresmo will face third-seeded Sharapova in the semis while Zvonareva takes on Petrova.