HARRISON, 13 Jun 2015 (AFP) - Kim's eight-under total of 138 gave her a one-stroke lead over Australian Hall of Famer Karrie Webb and two-time defending champion Park In-Bee, also of South Korea.
Webb birdied the 18th hole to cap a 71 and was joined on 139 by Park, who had five birdies in her five-under 68.
Not only is Park trying to win a third straight title in the second women's major of the year -- formerly known as the LPGA Championship -- she's closing in on the world number one ranking of New Zealand teen Ko.
Ko struggled to a three-over 76 for a two-over total of 148 and missed the cut for the first time in her pro career -- ending her streak of 53 straight LPGA cuts made.
Leading second-round scores on Friday in the Women's PGA Championship, the second major of the 2015 LPGA season (USA unless noted, par-73):
138 - Kim Sei-Young (KOR) 70-68
139 - Park In-Bee (KOR) 71-68, Karrie Webb (AUS) 68-71
140 - Suzann Pettersen (NOR) 74-66, Brooke Henderson (CAN) 67-73
141 - Stacy Lewis 70-71, Jenny Shin 66-75
142 - Gerina Piller 72-70, Caroline Hedwall (SWE) 71-71, Candie Kung (TPE) 70-72, Cristie Kerr 70-72, Lexi Thompson 70-72, Charley Hull (ENG) 68-74
143 - Morgan Pressel 73-70, Julieta Granada (PAR) 72-71, Mo Martin 72-71, Kris Tamulis 71-72, Azahara Munoz (ESP) 70-73, Jennifer Song 70-73
144 - Dori Carter 72-72, Lee Mi-Rim (KOR) 72-72, Ryu So-Yeon (KOR), Marina Alex 72-72, Anna Nordqvist (SWE) 71-73, Joanna Klatten (FRA) 70-74, Chella Choi (KOR) 70-74, Kim Hyo-Joo (KOR) 70-74, Sandra Gal (GER) 70-74, Jane Rah 70-74, Brittany Lincicome 70-74, Karine Icher (FRA) 69-75