Jung Yeon Lee, who held a share of the 36-hole lead, got to 10 under on her round but struggled down the stretch to finish alone in third place at 7-under-par 209 after a round of 71.
Amateur sensation Michelle Wie was one shot further back at 6-under-par 210 along with Karrie Webb.
Wie, who played in the final group of this event last year, has been impressive all week in her second appearance at this major championship.
'Last year I didn't really have a specific goal because I didn't know how well I could shoot,' said Wie. 'And this year I think I have a more specific goal. Like this time I am trying to win it or be in the top five, at least.'
The 14-year-old jumped out of the gate with birdies on her first two holes. At the par-4 10th, Wie dropped her approach inside 14 feet and drained the birdie putt en route to a bogey-free round of 69.
Park, who can lift herself unto the upper echelon of women's golf with a victory on Sunday, began the day three strokes off the lead at Mission Hills Country Club.
The Korean parred her first six holes before catching fire around the turn. Park ran off four consecutive birdies starting at the par-4 seventh and took hold of the outright lead as Lee's fine round was derailed on the back nine.
At the par-4 16th, Park played her approach to the back fringe within 17 feet of the cup and drained the birdie putt. The four-time LPGA winner then parred her two remaining holes to secure her share of the 54-hole lead.
'Today it was just really easy out there,' said Park. 'Obviously the condition was much easier than yesterday. My ball striking has been good all week and I just felt like this was the day to attack, get aggressive and move up the leaderboard.'
Song, who held the lead after the opening round, had fallen behind the leaders after a 73 on a windy Friday.
The 17-year-old LPGA rookie tallied back-to-back birdies from the second to move to 7 under but found trouble with a bogey at the par-4 sixth.
Song faltered again with a bogey at the 11th but managed to recover with a birdie at the very next hole.
She got back to minus-7 with a birdie at the 14th and drained a long birdie putt at the par-3 17th to match Park after a round of 69.
'My goal was to shoot 3 under. And I did that,' said Song, who would become the youngest player to win a major on the LPGA Tour should she come out on top on Sunday. 'I think I set myself up for a pretty nice day tomorrow. Exciting day, I've always dreamt about this and that's why I worked so hard to get to where I am.'
Lee was steady early on with three birdies on the front nine before a birdie at the 11th gave her a three-shot lead over the field.
The 25-year-old, who fired a 60 in the opening round of the Welch's/Fry's Championship earlier this year, game back to the field at the par-3 14th after her tee shot bounced in the water.
Lee walked away with a double-bogey and dropped another shot with a bogey at the 17th to finish one shot back.
Rosie Jones shot a 71 to join Wendy Doolan and Stacy Prammanasudh in a tie for sixth place at 5-under-par 211.
Dottie Pepper, who shared the second-round lead with Lee, struggled to a round of 74 to finish one shot further back at 4-under-par 212.
Annika Sorenstam's quest to win the single season grand slam seemingly failed to get off the ground. The Swede posted a 3-under 69 on Saturday to finish eight shots off the pace at even-par 216.