Pinehurst No 2 has proven tough to negotiate for many this week and Ko has been left to rue a six-over 76 during her first round, which basically took her out of contention for the tournament.
Her round of 71 today (sun) included three birdies and four bogeys and the 17-year-old is now in a share of 23rd place at eight-over.
Co-leaders Amy Yang and Michelle Wie, who are at two-under, are the only players under the card.
Ko could book a top-20 finish with a solid fourth round.
Meanwhile, Manawatu's Tim Wilkinson remains in contention at the Travelers Championship in Connecticut on the PGA Tour.
The left-hander fired a three-under 67 in his third round and is in a share of seventh place at nine-under for the tournament, four strokes back from leader Ryan Moore (-13).
Wilkinson has never won on the PGA Tour and a top-10 finish would be a nice boost for his season.
