Two-time major winner Brooke Henderson of Canada and Ruoning Yin and Xiyi Lin of China were a shot back as Baltusrol yielded just 16 under-par rounds to the field of 156 players.
The 42-year-old Pace won her lone LPGA Tour title in 2014 in China. She’s playing in her second event in the United States this year.
Wichanee Meechair of Thailand was alone at 68. Leona Maguire of Ireland, the winner last week in Michigan, was at 69 with Ayaka Furue and Yuka Saso of Japan, Jenny Shin of South Korea, Celine Borge of Norway and Esther Henseleit of Germany.
Rose Zhang, the two-time NCAA individual champion at Stanford who became the first player in 72 years to win an LPGA Tour event in her pro debut this month at nearby Liberty National, opened with a 70.
World No. 1 Jin Young Ko and Lilia Vu, the only two-time winners on the LPGA Tour this year, shot 72. No. 5 Minjee Lee also had a 72.
Defending champion In Gee Chun was 2 under at the front nine, but had five bogeys on the back nine and finished at 74.