Kim leads four-time defending champion Annika Sorenstam by one stroke. Sorenstam, who is trying to become the first person on the LPGA or PGA Tour to win an event five straight times, shot 6-under 30 on her opening nine. She could only manage two more birdies on the back nine to end one stroke back.
Japanese LPGA Tour player Shiho Ohyama stands alone in third place at 7-under-par 65. A pair of Koreans -- Il Me Chung and Women's British Open champion Jeong Jang -- around one stroke further back at minus-6 at Seta Golf Course.
Sorenstam came right out of the gate with a birdie on the first. After parring the second, the Swede birdied the third and fourth to move to minus-3. She made it three straight with a birdie on the par-5 third.
The 34-year-old ended a run of four straight birdies at the sixth as Sorenstam played the opening six holes in minus-5. She parred the seventh, then came right back to birdie the par-4 eighth.
Sorenstam parred nine, then got to 7-under with a birdie on No. 10. She parred her next three holes before securing the lead at minus-8. However, Sorenstam could only par out to end there.
Kim, who has 12 top-10s over the last three years, but no wins, started on the back nine and opened with a birdie. She picked up birdies on the 14th and 17th to head to the front nine at minus-3.
The 25-year-old Korean parred her first two holes on the front nine. She then dropped in her fourth birdie on the par-4 third. Kim caught fire at the fifth.
She birdied the par-3 and came right back to birdie the sixth to move to 6-under.
Kim was not done. She birdied the seventh and eighth to join Sorenstam in the lead at 8-under. Kim ended with another birdie on the ninth, her fifth straight, to lead by one at minus-9.
Laura Davies and Karrie Webb each carded rounds of 5-under-par 67. They share sixth place with Sophie Gustafson, Soo-Yun Kang, Yun-Hee Ku, Meena Lee, Jenny Rosales and Sung Ah Yim.
Grace Park and Gloria Park each posted rounds of 4-under-par 68. They were joined there by six other players.