Carlsbad:

Patty Schnyder claimed her second straight upset with a 6-4, 6-4 victory over No 4 seed Nadia Petrova to advance to the semi-finals of the Acura Classic on Friday.

Top-seeded Maria Sharapova of Russia had little trouble in a 6-2, 6-1 victory over Sania Mirza of India. Sharapova will play No 3 seed Anna Chakvetadze of Russia, a 6-7, 7-6, 6-2 winner over 10th-seeded Venus Williams. No 9 seed Elena Dementieva of Russia defeated countrywoman Maria Kirilenko, 6-2, 6-4 for a semi-final berth against Schnyder.