Pettersen, who fired a hole-in-one during her second round to claim a five-shot lead, bogeyed three of her first five holes at Sunrise Golf and Country Club before fighting back to card a one-over 73.
That left the Norwegian six under par and four shots clear of Spanish pair Azahara Munoz and Carlota Ciganda and South Korea's Sun Young Yoo heading into Sunday's final round.
"I had a great warm-up, felt good," Pettersen said. "On the second, I kind of made a little amateur mistake trying to get too cute on the tee ball and left myself with a very tough up and down.
"I just couldn't get it going and made a few errors. Today was a tough day for me. It was all about hanging in there and trying to bring it back to where I started.
Pettersen hit back with birdies at the eighth and 13th before another bogey on the 17th, but finished her round in style with a birdie on the last.
"I could easily have lost it out there today," the Solheim Cup star added.
"Some days are easy, some days are not that easy, some of the times you see everything you're going to do right in front of you. Other times you fall inbetween clubs and are not quite sure and then you start questioning if it's enough."
Munoz's 69 was the joint lowest score of the day and featured one bogey and four birdies, while Yoo and Ciganda both shot 72.