Just 35th on the money list, Park carded an 8-under par 63 at the Wykagyl Country Club and shared the third-round lead with Sweden's Annika Sorenstam, who posted a 7-under 64.
Park, who earned her only career victory last year at the Williams Championship, and Sorenstam completed 54 holes at 12-under 201. They held a two-shot advantage over South Korea's Hee-Won Han, the 2001 LPGA Rookie of the Year.
Han carded a 5-under 66, leaving her two strokes ahead of Australian Karrie Webb. Second-round leader Kelli Kuehne struggled to a 2-over 73 and dropped into a five-way tie for fifth with a Diana D'Alessio, Beth Daniel, Chris Johnson and Nancy Scranton.
In the driver's seat for a fifth Player of the Year award, Sorenstam already has won six times in 13 starts this season. She began the day three shots behind Kuehne.
Sorenstam has earned $1,894,054 this year, almost $800,000 more than Juli Inkster, who is second on the money list.