Pace signed for a five-under-par 66 at Baltusrol Golf Club in New Jersey to snatch a one-stroke lead over Canada's Brooke Henderson and Chinese pair Xiyu Lin and Ruoning Yin.

Grace Kim is the best-placed Australian in a tie for 12th at one-under, while Minjee Lee opened with a one-over 72.

Pace, 42, was one-under at the turn then began her string of birdies at the par-4 11th hole.

She picked up another shot at the par-3 12th and went top of the leaderboard on her own with a birdie at the par-5 18th.

Pace's best finish in a major was a tie for sixth at the 2015 Evian Championship.

“You know, I haven't had the best season in Europe. Mainly because I didn't practice hard enough if I have to be completely honest,” Pace said.

With little form to show, South African Pace leads after round one. PHOTO: Scott Taetsch/PGA of America via Getty Images.

“I started practicing for ShopRite, that event, a lot more. I just spent a lot more time-out there, and I'm feeling super confident in my game.”

Henderson, who won the 2016 Women's PGA, started on the back nine with two birdies and a bogey before closing strong with birdies at the 1st, 6th and her final hole of the day, the par-3 9th.

Henderson is vying for her third career major after also winning last year's Evian Championship.

Lin had a pair of birdies on each side and no bogeys during her opening round. She had a birdie on the par-4 13th hole and the par-5 17th to finish off her 67.

Her best major result was a tie for seventh at 2021's U.S Women's Open.

Yin, who has never finished higher than 41st in a major, started on the back nine and reached the midway point of her round with a birdie at No.17 and an eagle three at the par-5 18th hole.

Thailand's Wichanee Meechai, who has yet to record a top-10 finish in a major, is alone in fifth place at three-under 68.

Starting on the back nine, Kim moved to two-under early in her round before slipping back to even with the card, then returning to red numbers with a birdie on her third-last hole of the day.

Lee was cruising along at one-under before making a dreaded double-bogey seven at the par-5 17th to end her round in a share of 33rd spot.

Fellow Australian Gabi Ruffels is one stroke further behind after opening with a 73.

Karis Davidson (74), 2019 PGA champion Hannah Green (75) and Steph Kyriacou (75) all need strong second rounds to work their way back into contention, while Sarah Kemp (77) and Su Oh (82) will need a very low round on Friday to make the halfway cut.