Venus Williams reaches WTA Stanford semis

Venus Williams has reached the semi-finals of the WTA tournament in Stanford, beating 17-year-old wildcard CiCi Bellis 6-4 6-1 in an all-American match.

The 36-year-old top-seeded Williams won the last of her 49 singles titles in Taiwan in February and will face Alison Riske on Saturday (Sunday AEST) in California.

Riske led fourth-seeded CoCo Vandeweghe 6-3 1-0 in another all-American match before her opponent 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.