The Norwegian's lead after day three in Kapolei, Hawaii was one stroke as she took her total to a 14-under 202.
South Korea's Hee Kyung Seo was just behind after hitting a 66 largely thanks to three straight birdies on the back nine.
Defending champion Ai Miyazato, who was a stroke behind Pettersen at the beginning of the day, was a further two shots back in third after a 70.
Pettersen started the round with three birdies on the opening three holes before she reached 14 under with another at the seventh. A bogey on the eighth was soon cancelled out with another birdie at the 14th.
The world number six is looking to add to her Ladies European Tour win last month in China.
Stacey Lewis, the world number two, had a 69 to slot in at nine-under alongside teenager Ariya Jutanugarn, the 17-year-old first-round leader, and Lizette Salas.
- Sports & Recreation
- Hee Kyung Seo