Washington, August 3: Venus Williams remains on course to reach the final of the Silicon Valley Classic for the ninth time, 20 years after her first appearance in the decider of the WTA Premier event.
Venus lost to Lindsay Davenport in the final in 1998 and 1999, before gaining revenge by beating her compatriot to the title in 2000.
She overcame Kim Clijsters to win again in 2002, before losing to Davenport and Clijsters in 2004 and 2005 respectively.
Venus then lost finals to Marion Bartoli in 2009 and Johanna Konta two years ago, but she remains a force to be reckoned with.
Seeded third at the age of 38, Williams defeated Britain's Heather Watson 6-4 4-6 6-0 on Thursday to reach the quarter-finals.
Awaiting her will be Maria Sakkari, who thrashed eighth seed Timea Babos 6-0 6-1.
Fifth seed Mihaela Buzarnescu fared better, overcoming Amanda Anisimova 7-5 2-6 6-1.
Meanwhile, defending champion Madison Keys has been forced to withdraw from the tournament with a right wrist injury.
With Garbine Muguruza already having retired, Keys was the highest seed remaining in the WTA Premier tournament as she prepared for Thursday's meeting with Ajla Tomljanovic.
But hours before that match, the world number 12 followed in Muguruza's footsteps and pulled out.
"I am really sorry to have to pull out of the Mubadala Silicon Valley Classic," Keys said. "I have been feeling pain in my wrist over the last couple of days and felt worse today.
"This event is one of my favourites and I was looking forward to playing here in San Jose, but want to thank San Jose State University and Mubadala for pulling it together in such a short amount of time.
"I am excited to come back next year and play in front of your great fans."
Tomljanovic battled past lucky loser Magdalena Frech to win 6-4 3-6 6-3.