Australian Green, 22, hit four birdies in a four-under 68 to earn her first career lead at a major tournament.

England's Melissa Reid and Kim Hyo-joo of South Korea are one stroke behind.

Reid's three-under-par 69 included four birdies, after she dropped a shot at the opening hole at Hazeltine.

"I felt the weather was almost an advantage for us," said the 31-year-old. "People will look at my results and see my season hasn't been great.

"My preparation into this week has been really good. I'm feeling really good."

World number one Ko Jin-young was among those to struggle, finishing the day tied for 102nd at five over par.

The South Korean carded five bogeys in her round of 77, while five-time LPGA Tour winner Michelle Wie - on her return after two months out with a wrist injury - was left in tears after a 12-over-par 84.

"I was foolish to think I would shoot really well," said the 29-year-old American.

"It's just one of those situations where I'm not entirely sure how much more I have left in me - so, even on the bad days, I'm just trying to take time to enjoy it. But it's tough."

Two-time major winner Ariya Jutanugarn of Thailand and South Korean defending champion Park Sung-hyun were among six who carded two-under-par rounds of 70, while American Lexi Thompson, who won the ShopRite LPGA Classic earlier in June, is tied for 17th on level par.