"I pretty much kept it in play and putted amazing, that's the only way I could describe it today," said the 31-year-old American, who opened and finished her round with birdies.

In-Kyung Kim, Amy Yang and Jenny Shin all shot 66 to share a three-way South Korean tie for second place at Gullane Golf Club.

Seven-time LPGA winner Kim called it "a tough course but I think it suits my game."

Minjee Lee is the best-placed of the nine-strong Australian contingent after a four-under 67 left her tied for fifth.

Her bogey-free round included birdies at all three of the four par-5s and the par-4 14th.

Su Oh is a shot further back in a tie for 12th at three under after a 68.

Sarah Kemp and Katherine Kirk carded rounds of 70 be one under while Karrie Webb's even-par 71 has her tied for 43rd.

Minjee Lee shot four-under 67 to share fifth place at Gullane. PHOTO: Stacy Revere/Getty Images.

Sarah-Jane Smith and Rebecca Artis (both 74s), Hannah Green (76) and Whitney Hillier (77) all have work to do in the second round to make the cut.

Joh has yet to win in a decade on the LPGA Tour but she made the most of the hard, fast-running course to gain a significant advantage.

Defending champion Mi Hyang Lee opened her title defence with a three-over 74.

The youngest player in the field, 19-year-old Karoline Lund, posted a 67 and is tied for fifth in her first official LPGA event.

"It's so cool to just compete against those that have been your idols, like your whole life, and you've only watched them on television," she said.

"It's really nice to be here and compete against them and see how the level is."