Canadian Alena Sharp and Youngin Chun of South Korea share the LPGA's Marathon Classic lead at 7-under 64, a stroke ahead of Stacy Lewis and three others.
The 38-year-old Sharp carded eight birdies and a bogey, while the 19-year-old Chun had a bogey-free round. Both are seeking their first LPGA title.
Azahara Munoz, Caroline Masson and Jenny Haglund matched Stacy Lewis at 65 at Highland Meadows Golf Club in Sylvania, Ohio.