Suzann Pettersen set the early pace at the North Texas Shootout in Dallas where she holds a one-stroke lead following an opening five-under-par 66.
The Norwegian hit 17 greens in regulation, while posting two birdies in her closing three holes of a bogey-free round at Las Colinas Country Club.
A group of six players, including American Michelle Wie, are tied-for-second while Jodi Ewart Shadoff is the leading Briton.
The 26-year-old from Yorkshire is tied-for-11th - three strokes adrift - having reached four-under through 12 holes before back-to-back bogeys curtailed her charge.
Pettersen, who is chasing a 15th LPGA Tour title, is back in action following a back injury and she admitted: "I feel good. I've got to kind of pace myself a little bit. I can't do too much early in the week. So I have a lot of spare time to fool around with.
"I'm hitting the ball great. Today I was actually feeling a little bit tense to start, which is a good sign. So nice to be back."
Wie, who clinched her third LPGA Tour victory two weeks ago in her home state of Hawaii, had four birdies, two bogeys and an eagle in her 67.
She shares second spot with Cristie Kerr, Christina Kim, Caroline Masson, Cydney Clanton and Dori Carter.
She added: "It was a little bit cold in the morning but I'm happy with my round. I started off hot, and then I had a little three-putt, just couldn't get anything going after that, but you know, the eagle is always nice."
Defending champion and world No 1 In-Bee Park of South Korea is tied-for-35th following a level par 71.
Park's card was marred by a double-bogey six at the par-four 15th and she confessed: "I hit it into the water once today and I hit it out of bounds once today.
"It was just one of those kind of days. Nothing went really wrong but just a couple of bad shots that really penalised me."