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.”