Ko carded a 4-under 68 during the third round in Williamsburg, Va., to draw even with Lewis, who shot a 1-under 70 Saturday. Both will tee off Sunday at 8 under, tied for third place and five shots behind leader Lizette Salas.
With world No. 1 Inbee Park not in the field this week, the top spot in the rankings is very much up for grabs. Lewis, who won her last start at the North Texas LPGA Shootout, entered the week at No. 2 and can pass Park with a win or a solo second-place finish. The 17-year-old Ko, who won last month at the Swinging Skirts LPGA Classic, would become the youngest top-ranked player in either the men's or women's game with a win Sunday.
Ko will play in the penultimate pairing alongside Australian Katherine Kirk, while Lewis will tee off one group ahead of her along with Pornanong Phatlum, who is tied for sixth at 7 under. Salas, who grabbed the lead with a 6-under 65 in the third round, holds a three-shot lead and will play the final round with Hee Young Park.
Other players in contention through three rounds include former world No. 1 Yani Tseng and major winner Lexi Thompson, who are both tied for sixth at 7 under and trail Salas by six shots heading into the final round.