After claiming back-to-back wins in the tournament formally known as the LPGA Championship, the world number two is looking to join Annika Sorenstam as the only players to win the event three times in a row.
While Park was faultless in her round of seven-under, she was helped by a late slip by overnight leader Sei-Young Kim who bogeyed the last after three-putting from 12 feet.
Park, who climbed to 14-under, made light work of the Westchester Country Club as she and Kim pulled clear of the field, with Suzann Pettersen, Karrie Webb and Brooke Henderson next best on eight-under.
Kim's late stumble will be all the more frustrating as she had played well for the majority of her round. Back-to-back birdies on the opening two holes briefly saw her one-shot lead briefly doubled to two. A birdie at the ninth was cancelled out by a bogey at the next hole, but further birdies at the 12th, 15th and 16th saw her remain level with Park prior to her blemish at the 18th.
Park was calm and composed throughout, registering three birdies on the front nine to take the turn in 33 before adding a further four birdies on the back nine. A birdie from Park at last coupled with Kim's bogey saw the 26-year-old carve out a two-shot lead.
Webb had begun the day one shot off the pace of Kim, but bogeys at the first two holes saw her fall further back. However, the veteran Australian was able to ready the ship with four birdies and just a single additional bogey in a round of 72.
Henderson and Pettersen carded rounds of 71, with the latter enduring a rather up and down round that included a double-bogey-eagle run from the 11th to the 12th.