With Suzann Pettersen, her closest challenger going into the final round, struggling, Choi was hardly troubled as she went around in three under par, dropping a shot on the 10th but sprinkling in four birdies to hold off the chasing pack.
Fellow South Korean Inbee Park did her best to put the pressure on with an outstanding back nine, picking up six shots in the space of seven holes to card a 65.
Park birdied all but the 10th, 11th and 14th holes on her way back to the clubhouse, enough to push her clear into second place.
Karrie Webb recovered from yesterday's disappointment to take third place, two shots further back from Park after a round of 68.
She birdied the 18th to pull out of a tie with Ai Miyazato and Pettersen, who finished eight under par for the tournament.
Pettersen had put herself in contention with a 64 yesterday, but could manage only a 70 today, her round marred by a double bogey on the 15th and bogeys on the seventh and 16th.