The South Korean posted a score of 7-under 64 on the day to bypass a three-way tie for second place between American Brittany Lang, China's Shanshan Feng and South Korea's Hee Kyung Seo at 8-under 134. Seven players were tied for fifth at seven-under par.
The second round was called due to darkness with seven players still on the course. The round will finish tomorrow when the cuts will be made for the top 70 golfers and ties. The cut line is 1-over par.
They were few spectators left when Park took the lead with the sun setting.
"I played great today," said Park. "I hit the ball very well and hit my short irons really good, so that gave a lot of opportunities. I obviously putted very good. Two days more like this would be very good."
Park noted that the course played differently on Friday than it did during the first round, where she opened with a score of 69.
"It was really different. I didn't find the fairways being soft, but the greens were much softer than yesterday," she said. "Yesterday, some of the holes, it was almost impossible to stop it so it was playing really tough. It was really windy yesterday too and today it was a lot calmer."
Park checked the leaderboard earlier Friday and saw that players were pulling off low scores and challenging for the lead.
"I thought the course was playing a little bit easier and I think that gave me a lot of confidence," she said.
Another player brimming with confidence is last season's Rolex rookie of the year, Seo. The 25-year-old finds herself one shot off the lead going into the weekend. She had to battle to be there, hitting a birdie on the 18th hole after a double bogey on 17.
She didn't seem fazed by it though.
"The wind was blowing really hard from left to right and I thought it was the right club; I hit a six iron. The ball just dropped down and kicked to the right and I couldn't find it," said Seo. "It's OK, it's only the second round."
Winning rookie of the year has Seo riding high into her sophomore season.
"I have a lot of confidence from that rookie of the year award and it's easier than the first year," said Seo. "I know a lot of courses and I'm getting used to the system, so I'm more comfortable out here."
Park's round was only matched by Stacy Lewis, who bounced back from 1-over par 72 Thursday to go seven-under today and move up to a tie for 12th place.
"I just putted a lot better," said Lewis. "I think yesterday I didn't have very good feel around the greens and I finally got some putts to go in today. It was actually a really easy day, so it was nice."
There will be some Canadian content on the weekend as Maude-Aimee Leblanc of Sherbrooke, Que., and Isabelle Beisiegel of Sainte Hilaire, Que., insured their spot for Saturday by finishing 1-under par 141.
Beisiegel, who came into the tournament as an alternate, was surprised to be one of the Canadians leading the charge.
"I could not be further from top Canadian ranking wise," she said with a laugh. "But I'm just excited to have had a couple of good days and I'm just really enjoying it."
Beisiegel said she was fortunate during her round, but battled to make the cut.
"I had a couple good bounces, too, but that's golf," said Beisiegel. "You're going to get some good breaks and bad breaks, but you just have to go through the adversity and just keep working at it and just see what happens."
Other Canadians making it through to the weekend are Hamilton's Alena Sharp, Charlottetown's Lorie Kane and Toronto's Rebecca Lee Bentham at 1 over.