Overnight leader Lewis, looking for her third LPGA title of the season, finished the day at 11-under after shooting a one-over 73, which included two bogeys and a double bogey on the back nine.
"I feel like I'm still in the tournament, and just got to make some putts tomorrow," said Lewis. "I shot 63 the first day, so I know I can play good out here. I'm not too worried about it."
Park made up the three-shot deficit from the second round with a 70, including four birdies and two bogeys.
American duo Karrie Webb (67) and Natalie Gulbis (68), along with young Korean amateur Hyo Joo Kim (69), were a shot behind the leaders.
Cheyenne Woods, Tiger Woods's niece, was six under after a round of 70.