World number 121 Ayaka Uehara had the shock clubhouse lead midway through the opening round of the ANA Inspiration – the LPGA Tour’s first major of the season.
The top 24 in the world rankings are in action at the tournament in California but it was Japan’s Uehara who set the early pace with a six-under-par 66.
Swiss amateur Albane Valenzuela is a shot off the pace after a 67.
World number seven Cristie Kerr hit a 68 to sit two shots behind Uehara.
Bronte Law is the highest-placed Briton to have completed her first round. The Stockport-born golfer is four shots off the lead after carding a two under 70.
Dame Laura Davies, who retired after an opening 82 in the Kia Classic last week due to an Achilles injury, had a difficult round as she signed for a nine-over-par 81.