Being held at the lower course at Baltusrol, Pace birdied her final hole to finish 5-under 66.

She started her round with seven pars and finished with five birdies in her final 11 holes.

Behind the 42-year-old was Chinese duo Yin Ruoning and Lin Xiyu.

Yin and Lin shot 67 along with Canadian Brooke Henderson.

With five birdies and one bogey, Henderson, a two-time major winner, finished at 4 under, including a birdie-2 at her final hole.

"The play against the best in the world and post a score like that, is something I’ll never forget," said Pace.

Young Rose Zhang did not have a great start but managed to turn it around in the end.

Struggling with the opening hole, the Stanford girl birdied her final hole to finish the round 1-under 70.

"From a young age, I was pretty poised, and pretty steady. But I do feel like I've also been trained to just be as steady as can be," said the two-time NCAA individual champion.

"My parents, my dad, my mom have taught me to just be flexible in any situation that I'm in, and I feel like with a lot of adversity coming at me from a young age, and doing a lot of different obligations, that has allowed me to really try to be as composed as possible.

"It just comes with practice and innate self, I guess. "

Thai player Wichanee Meechair was the only golfer occupying fifth spot with 68.

Leona Maguire of Ireland, Ayaka Furue and Yuka Saso of Japan, Jenny Shin of South Korea, Celine Borge of Norway and Esther Henseleit of Germany was at 69 after round one.