South Korean rookie Park Sung-Hyun fired a seven-under par 65 on Friday to take a two-stroke lead midway through the LPGA Volvik Championship in Ann Arbor, Michigan.
Park fired six of her eight birdies on the back nine on the way to a 12-under par total of 132 and a two-shot lead over Australian Minjee Lee and Norway's Suzann Pettersen. Lee carded a six-under 66 and Pettersen signed for a 67.
"I started birdie-birdie on the first two holes and after that I kind of lost it a little bit," said Park, who parred seven straight holes before picking up a stroke at the 10th to start a run of three birdies in a row.
"From that point on, I think my putting kind of came back alive," added Park, who notched seven victories on the Korean LPGA tour last year.
Although she leads the Rookie of the Year race with three top-four finishes, she doesn't feel she has played to her potential on the LPGA Tour this season.
"I've definitely felt the pressure and that's probably one of the biggest reasons why I haven't performed up to my standards this year," she said. "This week I'm able to let things go a little bit more and play my game."
Lee teed off early and notched a season-low 66 that had her atop the leaderboard for much of the day.
Pettersen was surprised to find herself at 10-under given how little she has played this year.
"I usually play good the more tournaments I play, and last week was my first after a little bit of a break," Pettersen said. "My game is starting to shape up. Playing good golf, hitting a lot of good putts. Just enjoying this golf course."
China's Feng Shanshan, Australian Sarah Jane Smith and Americans Lizette Salas, Cydney Clanton and Jennifer Song were three shots off the lead on 135. South Korea's Lee Jeong-Eun was alone on 136.
South Korea's Ryu So-Yeon made the cut on the number at one-under par -- stretching her streak of cuts-made to 64 events, a run dating back to 2014.
After a first-round 72, Ryu was in trouble early with bogeys at two of her first three holes.
After a birdie and one more bogey put her at two-over for the tournament she got back to even with an eagle at the par-five 14th, and picked up what proved a crucial birdie at 17.
Notable names who won't be around for the weekend include two-time major winner Chun In-Gee, Kim Sei-Young and American Michelle Wie.