Top-seeded Venus Williams reached the Bank of the West Classic semifinals, beating 17-year-old wild-card entry CiCi Bellis 6-4, 6-1 in an all-American match Friday night.

The 36-year-old Williams won the last of her 49 singles titles in Taiwan in February. She won the Stanford event in 2000 and 2002.

Williams will face Alison Riske on Saturday at The Taube Family Tennis Center. Riske led fourth-seeded CoCo Vandeweghe 6-3, 1-0 in another all-American match when Vandeweghe retired because of an ankle injury. Vandeweghe was taken off the court in a wheelchair.

Second-seeded Dominika Cibulkova of Slovakia and third-seeded Johanna Konta of Britain also advanced.

Cibulkova beat fifth-seeded Misaki Doi of Japan 7-5, 6-0. The 2013 champion won the final 11 games after falling behind 2-5 in the first set.

Konta beat China's Zheng Saisai 6-2, 4-6, 6-3.