Ko ended up with a one-shot advantage over second-round leader In-Kyung Kim, shooting a 4-under 68 in unexpected calm conditions at tree-lined Mission Hills to reach 8-under 208. "If a little bit miss shot, It's OK," Ko said. "I'm not robot. I'm human. Don't think about bad things. Just looking for good things."
Kim birdied the par-5 18th for a 73. She gave herself a chance to win the event seven years after missing a 14-inch putt on the final hole of regulation and losing to Sun Young Yoo on the first hole of a playoff.
"To be honest, it's good to have three-shot lead going into the tournament today because I quite lost it," Kim said. "I don't know what it is. I guess it's just expectations that I didn't know I could live up to, maybe."
Four strokes behind fellow South Korean player Kim entering the round, Ko walked off the 10th green with the five-shot lead after a quick three-stroke swing. Ko holed a 25-foot birdie putt on the par-4 10th minutes after Kim snap-hooked a drive into the right-side trees and made a double bogey on the par-5 ninth.
"The wind didn't really come as much as I expected," Kim said. "I think that kind of got me a little bit on the front nine. I was tough on myself, but tomorrow is another day. I've learned a lot today, so hopefully that will teach me going into tomorrow."
Kim rallied to birdie the 10th, her first birdie of the day after making eight of them in a second-round 65, and pulled within two strokes when Ko hit into the water short of the green on the par-3 14th and made a double bogey of her own.
Ko followed with a bogey on the par-4 15th, cutting her lead to a single stroke. Ko pushed the margin back to two with a 10-foot birdie putt on the par-3 17th. She missed a 10-foot birdie try on 18. "I had great round still," Ko said. "Sometimes that happen on No. 14 and 15, also, but I had birdie on 17. It was really pressure to me, but I can do. Doesn't matter. I'm not afraid everything. I'm just looking forward to Sunday."
Kim closed with a 5-footer on 18 in the final group. "I did my best," Kim said. "I still love playing golf. That's why I'm out here. I think that's why I played quite well on the back nine, I hit many good shots. I really enjoyed golfing. Things get a little hard, but I'm surprised that I'm still close to the lead."
Mi Hyang Lee and Danielle Kang were 5 under. Lee had a hole-in-one on 17 and birdied 18 in a 68. "Was good comeback," Lee said. "Feels like roller-coaster." Kang shot 70. "It's the toughest it's ever played in my opinion," Kang said. "I've been here I think eight years now. The rough is incredibly long. Greens are firm and slick. It's tough."
The 23-year-old Ko won the Founders Cup two weeks ago in Phoenix for her third LPGA Tour title and leads the money list. She tied for second last week in Carlsbad for her fourth top-three finish in five events this year.
Ko spent five weeks in the offseason practicing in the area. "I had couple rounds on this course with my coach," Ko said. "I practice hard in the Palm Springs in January. About my swing, fix a little bit, and then putting or short game, training, everything. ... But in January, was really difficult weather and different weather now. Was really cold and then huge wind."
The 30-year-old Kim struggled with the 2012 loss at Mission Hills before finally ending a long victory drought late in 2016. Her confidence restored, she won three times in 2017, capped by a major victory in the Women's British Open.
Ko played the front nine in 5-under 31. She birdied the par-5 second, ran in a 40-foot birdie putt on the par-4 fourth and tied Kim at 7 under with an 8-footer on the par-3 fifth. Ko pulled ahead with a 6-foot birdie putt on the par-4 sixth. She increased the lead to two shots with a birdie on No. 9, hitting a wedge to 6 inches.
Canadian Alena Sharp had the best round of the day, a 67 to join Jeongeun Lee6 (71) and Katherine Kirk (74) at 3 under.
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