The world no.17 was thrilled to complete the back nine holes in four-under par.
"I think that is harder [than the front nine]. The two birdies were a great way to finish."
"John", a local caddy, also helped with his intimate knowledge of course measurements and conditions.
"The course is largely flat but the greens are undulating so it was good getting help in pressure positions," Ko said. "That flatness means it is harder to see dangers like bunkers. He also helped me line up to the target."
Ko's Mum Bonsuk and coach Guy Wilson observed the teenager's progress first hand.
Wilson says the use of the local caddy was a conscious move.
"As an amateur Lydia doesn't have someone on the bag week-to-week so it's important to pick someone who's a good fit. Knowledge about playing the right lines and conditions are vital. John has done that so far."
The coach admitted to being a touch nervous early.
"Especially with the double bogey. She had a rare poor tee shot, got a bad bounce and paid the price. I thought 'oh God, the last thing we want is to be making plans to leave early', but Lydia kicked herself into action and made a string of birdies.
"She played patient golf. Inside she might've been angry but I don't think you'd ever see any of it. The driver tends to be one of her safe clubs, she doesn't hit too many wide ones. If you miss a fairway here you're looking at bogey straight away."
After a spot of lunch, the afternoon was spent working on her pitching and putting.
"The greens were damp and quite skiddy. We've got to manage that better if it rains tomorrow," Wilson said.
Patchy drizzle became heavier later in the afternoon before fining up. Ko finished her round shortly after midday so missed the worst of it.
Ko has three top-40 finishes at the majors this season - a tie for 25th at the Kraft Nabisco championship, a tie for 17th at the Wegmans LPGA championship and a tie for 36th at the women's United States Open. The final major, the Evian championship, will be held in France next month.