SINGAPORE, 7 Mar 2015 (AFP) - South Korea's Park remained bogey-free for the tournament as she fired four-under 68 for an aggregate score of 203, putting her ahead of Ko and Stacy Lewis who shared second.
Their positions mean the world number one, two (Park) and three (Lewis) will make up Sunday's final grouping in what could be a tight finish at Sentosa Golf Club.
"It will be great fun," Lewis said of the match-up. "It's great for the fans and for our tour. This leaderboard all week has been unbelievable."
Seventeen-year-old Ko, the youngest number one in golfing history, hit five-under 67 as she scents her third win in a row after the Australian Open and New Zealand Open.
"Yeah, that would be I guess a dream three weeks, but I'm just going to try my best," Ko said. "The girls are playing good golf and it's a tough course.
"Just one shot can cost you a couple."
Azahara Munoz, Anna Nordqvist and Suzann Pettersen were also in the hunt, lying four shots off the lead in tied fourth position.
Park's prime target is regaining the world number ranking, after being toppled by Ko last month, but the 26-year-old vowed not to put herself under too much pressure.
"I want it, I just know I want it, but I'm just not going to push myself too hard to get something," Park said. "I mean, it’s something that if you push for, it's just hard to get.
"Just a couple of wins and playing great golf and it's going to come. So I'm just going to not rush anything and just play good golf."
Park has been top of the leaderboard all week but her co-leaders after round one and two, Tseng Ya-ni and Carlota Ciganda, now lie nine and six shots back respectively.
Round three scores from the HSBC Women's Champions at Sentosa Golf Club in Singapore on Saturday (par-72):
203 - Park In-Bee (KOR) 66-69-68
205 - Lydia Ko (NZL) 68-70-67, Stacy Lewis (USA) 69-69-67
207 - Azahara Munoz (ESP) 70-67-70, Anna Nordqvist (SWE) 69-70-68, Suzann Pettersen (NOR) 71-68-68
208 - Ryu So-Yeon (KOR) 70-69-69
209 - Carlota Ciganda (ESP) 69-66-74, Feng Shanshan (CHN) 70-71-68, Jessica Korda (USA) 72-67-70
211 - Jenny Shin (KOR) 68-70-73, Caroline Masson (GER) 71-68-72, Lizette Salas (USA) 70-72-69
212 - Danielle Kang (USA) 70-70-72, Tseng Ya-ni (TPE) 66-75-71, Karrie Webb (AUS) 68-70-74, Choi Na-Yeon (KOR) 71-74-67, Brittany Lincicome (USA) 74-71-67