Kerr, who has won twice previously at Kingsmill Resort & Spa, finished 54 holes at 10-under-par 203.
One shot further back was Angela Stanford, who carded a 2-under 70, while Ilhee Lee registered a third straight 69 to grab sole possession of fifth place at minus-6.
Second-round Ariya Jutanugarn tumbled to a 2-over 73, dropping into a sixth-place tie with Lizette Salas (65) at 5-under 208.
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