Stanford - Wimbledon winner Serena Williams swept past tenacious teenager Nicole Gibbs 6-2, 6-1 on Wednesday in her opening match at the WTA Stanford Classic.
World number four Williams was fighting off jet lag as well as reigning US college champion Gibbs, an American ranked 403rd in the world and a junior at Stanford University, host of the $740 000 hardcourt event.
It took defending champion Williams, who enjoyed a first-round bye, only 62 minutes to advance, even though Gibbs - playing in her first WTA main draw - saved three match points over two games before going down to defeat.
"I couldn't quite believe I was playing today, but I'm healthy, I have a heartbeat, so there was no reason not to," Williams said.
"I'm sure I'll feel better after a day off. I've been waking up at 02:00. I was sluggish today, but it was fine to get that win over with."
Williams said she had no trouble adjusting to the hot weather in northern California.
"The weather is definitely different than London with all that gloom and clouds," she said. "My body is used to the conditions here."
Williams, winner of 14 career Grand Slam singles titles, will next play a Friday quarter-final against South African sixth seed Chanelle Scheepers, who beat Portugal's Michelle Larcher de Brito 6-3, 6-4.
American Coco Vandeweghe, ranked 120th in the world, produced the first big upset of the week with a 6-4, 6-2 victory over former world number one Jelena Jankovic - who double-faulted to set up a match point.
The defeat was the third straight in an opening round for the Serb, who just began working with her third coach this season in an effort to rescue a ranking which has fallen to 20th since she topped the WTA list in 2008.
Belgian fifth seed Yanina Wickmayer ended the British challenge for the week with her 5-7, 6-1, 6-4 defeat of Heather Watson.
Williams returned to California on Monday, arriving 48 hours after winning her fifth Wimbledon title. She will return to Europe late next week to train in Paris before traveling to the London Olympics, which begin on July 27.
The 30-year-old American, saying she is in the best shape of her career, was pleased to get her job done against Gibbs.
"She played really well. She moves well and doesn't quit," Williams said of Gibbs. "That's the best quality you can have as a tennis player.
"It's good to see such Americans coming up. She played a good game and was focused all the time. I was surprised that she didn't have many nerves.
"It was not a beatdown for me. She really held her own."
Results on Wednesday from the third day of a $740 000 WTA hardcourt tournament (x denotes seed):
Serena Williams (USA x1) bt Nicole Gibbs (USA) 6-2, 6-1
Coco Vandeweghe (USA) bt Jelena Jankovic (SRB x4) 6-4, 6-2
Yanina Wickmayer (BEL x5) bt Heather Watson (GBR) 5-7, 6-1, 6-4
Chanelle Scheepers (RSA x6) bt Michelle Larcher de Brito (POR) 6-3, 6-4