Australia's Ajla Tomljanovic has advanced to the quarter-finals of the Silicon Valley Classic after rallying to defeat Poland's Magdelena Frech in three sets.
The world no.64 took an early lead but dropped the second set before prevailing 6-4 3-6 6-3 in a match lasting more than two hours.
The 25-year-old will now face Romanian fifth seed Mihaela Buzarnescu in the quarter-finals.
Tomljanovic was originally scheduled to face-off against defending champion Madison Keys in the second round until the American was forced to withdraw due to pain in her right wrist.
The hard-hitting 23-year-old, runner-up at last year's US Open where she lost to fellow American Sloane Stephens, is ranked no.12 in the world and was the second seed in San Jose.
"I am really sorry to have to pull out ... I have been feeling pain in my wrist over the last couple of days and felt worse today," Keys said.
Meanwhile, Venus Williams has also secured herself a spot in the quarter-finals after fending off the efforts of Brit Heather Watson 6-4 4-6 6-0 in the second round.
"It was a tough match and she played incredible," Williams said on court.
"There were times when I had no answers ... (I just wanted to) control the points and enjoy the battle, just get out there and try do what I know that I can."
Third-seeded Williams is the highest remaining seed after the withdrawals of Spaniard Garbine Muguruza and Keys due to injuries.
Williams will now go up against Greek Maria Sakkari, who also made the last eight after winning 11 straight games to dispatch Hungarian Timea Babos 6-0 6-1.
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