She also had a mixed day with her putter. She opened with a birdie and said she putted well for nine holes, then not so well, before making a long birdie putt on her last hole, the par-3 ninth.
"I didn't hole many putts and didn't even give it a good chance on some of them which was a little silly."
She admitted having doubts over some of her putts as she struggled to read the lines on Clearwater's contoured greens. "I wasn't confident with my read on some holes, there were questions marks in my head - I doubted myself a little bit and got angry a little bit - but they are not the easiest greens to read here and if there's doubt that's the last thing I need."
Asked what she was going to do fix her minor flaws, Ko replied: "I'm going to have some food - even in my yardage book it says 'even if things don't go well you gotta eat', that's what I write - I eat a lot on the course.
"So I'm gonna go eat, hit a few balls ... and have a good sleep."
Having said all, the world No. 1 is right in the mix for the defence of her title with two rounds to play.
More importantly she finished with a birdie on the par-3 ninth hole, her last of the day.
"Always the first shot and last shot of the day are the toughest. [On the first hole] there's people out there and they announce your name and the last hole sets the pace for what you might be thinking overnight."
Ko, 18, was particularly impressed a large fan base was on hand for her 8.14am tee time.
"At that time of the day, from the first hole, there were a lot of people here. Even if my favourite player was out there at 8am I wouldn't come out and start clapping for them which shows how much they support me and support this event."
She knows there will be even bigger galleries today when she tees off in the afternoon and admitted that while a huge support base was "exciting" it also brought some added pressure with "so many eyes on you wanting your ball to go straight".
First round leader Larsen admitted some surprise at Ko's relatively slow start.
"When she's not on the leaderboard you look for her and wait for her to come there. I'm sure she will be up there at the weekend."
Larsen, who was 12th here last year, claimed her maiden European title in Sweden last year, says she knows how to handle the big galleries should she end up alongside Ko in the final round.
"I've learned to handle crowds and being up there - I feel comfortable going into the weekend."