Women's world No. 1 Annika Sorenstam, making her first appearance on the LPGA Tour since the Women's British Open, is one stroke behind Kim at minus-5. She is joined there by rookie Shi Hyun Ahn. Another rookie, Reilley Rankin, posted a 4-under-par 67 for fourth place.
Kim started on Cedar Ridge Country Club's 10th tee and quickly moved into red figures as she drained a 9-foot birdie putt on the 10th. However, she missed a 6-foot par putt at the next to slip back to even par.
The 20-year-old nearly aced the par-3 13th as her tee shot came to rest within inches of the cup. She kicked in that birdie and got up-and-down for birdie at the par-5 14th.
Kim made it three straight as she rolled home a 40-footer for birdie at the par-3 15th. She ran off three straight pars before sinking a 3-foot birdie putt at the first.
Kim came back with a birdie at the third to move to 5 under. She converted a 15-footer for birdie at the seventh then parred her final two holes for the overnight lead.
'I was really fatigued coming into this round,' Kim said. 'I just sort of said, just chalk it up and just see what you can scrap together. I think one of the reasons why I played so well was because I probably hit 12 or 13 fairways, and part of that was my fear. I played out of Bermuda (grass) only a few times.'
Sorenstam dropped in back-to-back, 6-foot birdie putts at five and six to get her round going. However, she missed the green on Nos. 10 and 11 and was unable to save par either time dropping her back to even par.
The Swede regained her poise quickly. Sorenstam ran in a 6-foot birdie at the 12th and came right back with a 35-footer for birdie at the next.
Sorenstam made it three straight as she sank a 15-foot putt for birdie at 14. The 2002 winner here closed in fine fashion too. She hit 8-iron to both the 17th and 18th greens.
On 17, her second shot landed 25 feet from the hole and she made that putt. Sorenstam's approach at 18 came to rest 11 feet from the cup and she sank that too for a share of second.
'Well, I did rolled some putts in for sure,' said Sorenstam. 'I thought overall I played really well, but I made a few mistakes. I made two bogeys which I didn't make up-and-down, which I wish I would have. I had a lot of putts in the beginning that didn't go in, but on the back nine they did go in.'
Ahn matched Sorenstam's seven birdies and two bogeys. The Korean ran home a 30-footer for birdie on No. 1. Ahn converted back-to-back birdies from the seventh to move to minus-3.
At the ninth, Ahn's tee shot landed in the rough and she was unable to reach the green with her second. After chipping to 18 feet, Ahn missed the par putt. She responded with birdies on 10 and 11 to move to 4 under.
Ahn made it three straight at she rolled in a 21-foot putt for birdie at the 12th. Ahn moved to 6 under when she drained a 33-footer for birdie at the 15th. However, she bogeyed the 17th to slip back into second place.
Liselotte Neumann, Rosie Jones and Kelli Kuehne each opened with rounds of 3-under-par 68 to share fifth place. Mikaela Parmlid and Karen Stupples are one stroke further back at minus-2.