Serena Williams continued to breeze through the Bank of the West Classic as she booked her semi-final place with a straight-sets win over South Africa's Chanelle Scheepers.
Playing in Stanford the week after securing her fifth Wimbledon title, Williams admitted she was in something of a daze after winning her first match.
But she was in grand slam-winning form - in the second set at least - as she claimed a 6-4 6-0 win over Scheepers.
She will next face ninth Romanian seed Sorana Cirstea, who upset third seed Dominika Cibulkova 6-7 (5/7) 6-2 6-0.
Coco Vandeweghe sealed her first appearance in a WTA Tour semi-final with a 6-4 6-4 win over Poland's Urszula Radwanska.
The American only made it into the draw as a lucky loser, but has taken full advantage.
"I was pretty mad about losing in the last round in qualifying," Vandeweghe told the WTA Tour website. "I had the match on my racquet and didn't play well on that day - of course you can't play well every day.
"But I seem to be doing a pretty good job of picking myself back up and putting a lot of good matches together.
"I've been putting a lot of hard work in, on and off the court, and I knew it would translate into my matches sometime. And I'm glad it's here."
On her way to the semi-final, where she will play Yanina Wickmayer, Vandeweghe has beaten, among others, former world number one Jelena Jankovic, a moment she particularly enjoyed.
"I was definitely happy to finally beat Jelena," she said. "A memory I definitely keep is when I was 16, my first match on Arthur Ashe Stadium, opening night, she was number one in the world, just a huge experience.
"I remember the first serve I hit I aced her out wide and I was totally aiming up the T. I was thinking, 'I have no idea where this serve's going'.
"I was just so nervous. So to beat her two nights ago, I was so happy about that."
Belgian Wickmayer beat second seed Marion Bartoli of France 6-3 6-2.