Pak, the inspiration for a generation of Korean women who have made their mark on the LPGA Tour, is seeking her sixth major championship. She became the youngest player to be inducted into the LPGA Tour and World Golf Halls of Fame in 2007 at age 30.
She suffered her recent injury when she stumbled and fell during the week of the LPGA Tour stop in Mobile, Ala. This is her first competitive appearance since then.
Pak shot a 1-under 71 over the Locust Hill Country Club course for a 36-hole total of 3-under 141.
Tied for second at 142 were Inbee Park, Sandra Gal, Paula Creamer and Mika Miyazato.
World No. 1 Yani Tseng suffered through a rare off week and missed the cut by five shots with a 151 total. Tseng won this tournament by 10 shots a year ago.
Michelle Wie, her game having recently deserted her, shot an 82 and finished at 156. Wie has missed the cut in her last four stroke-play events.
Teen sensation Lexi Thompson reached 1-under for the championship during her round, but struggled on the back nine and wound up at 2-over 146.