Pak has won the tournament four times and finished in the top 10 four other times in the past nine years. She owns the course record at the Highland Meadows Golf Club -- a 61.
Her round Thursday left her two shots in front of Alena Sharp and four strokes ahead of Jin Young Pak. Defending champion Mi Hyun Kim shot a 68 and was part of a tie for fourth with Morgan Pressel, Aram Cho and Carri Wood.
"I feel great about this golf course," the leader said. "Everyone asks why. I don't know. I always feel great and really comfortable here. It seems like because I've won so many times, and have so many great memories about it, maybe that's why my game is a lot more solid on this golf course."
Pak, starting on the back nine, bogeyed her first hole. But she then ran off three straight birdies to get going.
She finished her round with birdie putts of 25 feet on the eighth and 10 feet on the ninth.