England's Jodi Ewart Shadoff carded a four-under-par 68 to share the first-round lead at the LPGA Kraft Nabisco.
Ewart Shadoff hit six birdies and two bogeys in the her opening round at the season's first major, which takes place at Mission Hills in California.
The 25-year-old from Yorkshire shares the lead with South Korea's Na Yeon Choi and Norway's Suzann Pettersen.
"I've been playing really consistently in the last three or four tournaments," said the Yorkshire-based player..
"I knew my game is right there, and I knew I was due to have a really good round."
Ewart Shadoff took the outright lead with four holes to play after four consecutive birdies starting at the par-five 11th, but dropped a stroke with her second bogey of the day at the 16th.
America's world number one Stacy Lewis stood one over par on 73, with number two Yani Tseng level par.