Hee-Won Han is alone in third place at five-under-par 139, followed by Michele Redman, who shot an even-par 72 Saturday and remains at four-under par.
Kim broke into red figures early with a tap-in birdie at the fourth hole. She made two additional birdies on the front nine, a 10-footer at the seventh and a 12-footer at No. 8, to make the turn at three-under 34.
Kim collected two additional birdies on the back nine. She knocked an eight- iron to 12 feet at the 12th hole and made it back-to-back birdies with a 10- footer at the 13th, but she needed solid bunker play down the stretch to preserve her cushion.
At the par-three 15th, Kim found the back bunker off the tee and blasted 15 feet past the hole. She drained that par save and once again holed a testy par save after finding a sand trap at 17.
Kim polished off her second consecutive round without a bogey and will try to erase past memories of having a big lead and not hoisting the trophy Sunday afternoon.
Six weeks ago at the Wegmans Rochester LPGA event, Kim squandered a five-shot lead on Sunday and lost the championship to Karrie Webb.
'But I couldn't sleep that night, Saturday night,' said Kim, referring to the event in Rochester. 'I lead by five shots, but I just worry about my shots, putting. I don't know.
'I'm very confident. I have to be smart.'
Ammaccapane was flawless Saturday with seven birdies and no bogeys and low rounds in Ohio have become the norm. She fired a career-low 62 in the final round of the Jamie Farr Kroger Classic three weeks ago and opened the Giant Eagle LPGA Classic with a 65.
'I'm putting together some good rounds of golf,' said Ammaccapane. 'The putter has been the big difference. I changed a couple things. It feels good in my hands. When I see the line, it's all feel for me. Some days with putting, it can be very awful. But it's been pretty good for a while. When I'm bad right now, it's not really all that bad.'
Candie Kung (68), Pat Hurst (72), Lorie Kane (73) and Rosie Jones (75) share fifth at three-under-par 141.
Anna Acker-Macosko (71), Betsy King (71), Yu Ping Lin (72) and Suzanne Strudwick (72) are tied for ninth place at minus-two.
First-round leader Mhairi McKay struggled badly on Saturday with an eight- over-par 80 and is tied for 22nd at one-over par.
The 36-hole cut fell at six-over-par 150 and 80 players advanced to Sunday's final round.