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The Kiwi opened her round with three straight birdies and was five-under through seven holes to sit in third place.
Ko sits two shots behind leaders Ariya Jutanugarn and Mariajo Uribe who both opened with eight-under rounds of 64.
Ko is a three-time winner of the event, twice capturing the title as an amateur.
Meanwhile Danny Lee has made a strong start to the Fed Ex Cup playoffs with an opening round four-under 67 at the Northern Trust event.
Lee sits in a share of fourth place, one shot behind a trio of leaders in Jamie Lovemark, Kevin Tway and Vaughn Taylor.
The Kiwi had three birdies on the back nine, after beginning his round at the 10th hole, and moved to five under with an eagle at the par five third hole. However he dropped a shot with his only bogey of the round two holes later.
Lee, who came into the tournament in 103rd place on the Fed Ex Cup standings, needs to be within the top 100 to advance to the next tournament.