The South Korean ended up clear of Choi Hye-jin, the 17-year-old amateur carding a 71 in her final round.
World number one Ryu So-yeon (70) and Hur Mi-jung (68) were tied for third at seven under.
Park, who opened the event with a 73, posted rounds of 67 on the weekend to secure her first win on the LPGA Tour.
She made three birdies before her only bogey of the final round – at the par-four ninth – before three more birdies on the back nine.
Choi produced a fourth consecutive round under par, but a double bogey at the par-three 16th cost her any chance of a stunning win.
Overnight leader Feng Shanshan slipped back into a tie for fifth after a 75.
The 27-year-old from China was joined by Spain’s Carlota Ciganda (70) and South Korean Lee Jeong-eun (71) at six under.
Protests were staged during the final round with United States president Donald Trump present at the course he owns.