Karine Icher posted a bogey-free 66 to grab the early lead at the Swinging Skirts Classic in Daly City, California.
The French player, who is yet to win on the LPGA Tour, is two strokes clear of the field in this $1.8m event.
Starting on the 10th tee at Lake Merced Golf Club, the 35-year-old made four birdies in her opening seven holes and added two more on the back nine.
Her closest challengers are New Zealander Lydia Ko, Koreans Ilhee Lee and Jenny Shin, American Maria McBride and Dewi Claire Schreefel of the Netherlands who all carded 68s.
The first day's play was brought to an early conclusion due to bad light, with more than 20 players still to complete their opening round including Spaniard Carlota Ciganda who was two-under-par through 14 holes.
Icher said: "It was just a good day. I'm happy about that. I stayed confident all through the round.
"I think the strategy on this golf course is to stay short of the hole. It's a tough golf course, especially with the wind and temperature. It gets so cold."
Teenage Brit Charley Hull and Scotland's former Open champion Catriona Matthew both opened their accounts with one-over-par 73s.