Venus Williams cruised past Vera Zvonareva 6-4, 6-3, and Serena Williams outplayed Anastasia Rodionova 6-1, 6-4. Unseeded Yan Zi of China also upset top-seeded Jelena Jankovic of Serbia 6-3, 3-6, 6-3 to reach the semis of the $600,000 tournament.
The Williams sisters - second-seeded Venus and third-seeded Serena - will play Saturday in their first match against each other since Venus beat Serena 7-6 (5), 6-2 in the 2005 U.S. Open. The two have split their 14 career meetings.
Yan's semifinal opponent will be fourth-seeded Patty Schnyder, who faced a strong challenge before downing Uzbekistan's Akgul Amanmuradova 4-6, 6-4, 7-6 (1) in the quarters.
"This is one of the best wins of my career, it's been a dream run," said Yan, who defeated eighth-seeded Maria Kirilenko of Russia in the opening round.
World No. 4 Jankovic struggled with her serve as Yan seized control of the match. Yan clinched the first set by breaking Jankovic in the eighth game and raced out to a 4-0 lead in the final set.
"I was struggling with my service in the first set," Jankovic said. "Then my shoulder began troubling me after the second set. I hope the injury is not serious."
Venus Williams built a 5-1 lead in the first set. She forced two breaks in the second set while dropping serve once.
"It was difficult to play Venus today," Zvonareva said. "I have a lot of work to do. I have not been at my best form and need to get better."
