Birdies were hard to come by Thursday on the slick, undulating greens and narrow fairways of Saucon Valley Country Club, which played at its full length of 6,740 yards.
Ochoa, looking for her first Womens Open title, had two birdies and two bogeys on her first nine, including a birdie putt of more than 50 feet on the second hole.
Kerr hit 15 greens and 10 fairways in a round of three birdies and a bogey.
Reynolds, a two-time winner on the Futures Tour, had four birdies and two bogeys.
Defending champ Inbee Park is among the afternoon starters.