After starting in a share of 16th today, Ko's round, which included six birdies and three bogeys, saw her move to a share of fifth place at five-under for the tournament.
The North Shore product was four shots back from leader Brittany Lincicome (-9), although a number of players are still yet to finish their round, which could influence Ko's position on the leaderboard.
Ko will have been pleased with her round after she opened with a frustrating two-under 70 yesterday that included five birdies and three bogeys.
The world No 2 is still searching for her maiden major crown and a win this week could also push her to the top of the world rankings.
"Winning would be great, but I'm just going to take it day by day," Ko told the LPGA Tour before the tournament.
"If it goes my way, great, and then I become world No 1, it's even better. But I'm not going to think about it. I'm just going to try and enjoy it and try to think of it as a normal, another LPGA event."
There are some big names near the peak of the leaderboard with the likes of Lexi Thompson, Inbee Park and Suzann Pettersen all well placed.
- Daniel Richardson of APNZ
