Serena Williams fought off fatigue to post a 6-4, 6-0 win over Chanelle Scheepers to reach the semi-finals of the WTA hardcourt tournament in Stanford.
Williams, the top seed and defending champion, won a 43-minute first set punctuated by five breaks of serve against her sixth-seeded South African opponent.
She said she was still feeling the effects of her triumph at Wimbledon last weekend and the subsequent flight to California.
"I still have major jet-lag," said the 30-year-old US star, who said she awoke in the early hours of Friday and watched a DVD of popular series "Desperate Housewives" .
"I've been up a long time," she said. "I'm tired now and ready to sleep, but it felt good to be out here -- and especially good to win.
"I didn't want to take anything, so I was wide awake just like as if I was in Europe. I started the match slow and sluggish, but I expected that. I just stayed in there until I began moving better.
"I told myself just to get through it, win quickly. I'm a fighter, I just click -- the mentality just kicks in."
Williams, whose first title upon her return last summer from a series of health problems came in Stanford, swept through the second set.
On Saturday she'll face Sorana Cirstea after the Romanian roared back to upset Slovak third seed Dominika Cibulkova 6-7 (5/7), 6-2, 6-0.
Yanina Wickmayer pounced on nine double-faults from Marion Bartoli to knock the French second seed out in their quarter-final.
Belgium's Wickmayer, seeded fifth, ousted Bartoli 6-3, 6-2 to advance to a final-four clash with American Coco Vandeweghe.
Vandeweghe reached the first WTA-level semi-final of her career with a 6-4, 6-4 victory over Poland's Urszula Radwanska.
Cirstea coped with a bevy of incorrect line calls in her match, but won six Hawk-eye electronic challenges.
"After that many, I didn't trust anyone anymore," she said. "I felt like someone was playing a joke on me. There were too many mistakes, I've never experienced this.
"It was just hilarious. It was everyone, not just one linesperson. The chair umpire didn't over-rule anything. I'm thankful we have this (Hawk-eye) system. It was important to stay in the match mentally."
The Romanian also helped her own cause with 15 aces and won the last 10 games on the way to victory.
Bartoli, the 2009 champion and runner-up to Williams last year, was plagued by errors in a match lasting just under 90 minutes.
She double-faulted twice in what proved to be the final game when she lost serve for the fourth time.
Bartoli saved the first match point she faced, but Wickmayer followed with a winner Bartoli couldn't reach.
It was world number 37 Wickmayer's first win over the 2007 Wimbledon finalist and world number 10 in four meetings.
Wickmayer, now into her fourth semi-final of 2012, kept Bartoli well off the top of her game.
"I was focused even when I was leading," said Wickmayer, a finalist at two tournaments this season. "I played some of my best tennis today."