Pettersen also had three bogeys on the day in a 6-under-par 66 for the lead over four golfers at 5-under with another 10 players just two strokes off the team.
Jessica Korda, who won her first professional title at the Women' Australian Open in 2012 and her second at the LPGA's 2014 season-opening event in the Bahamas Jan. 26, is among those tied for second. Also at 5-under 67 are Park Hee-young, Marion Ricordeau and Jaclyn Sweeny.
The group at 4-under includes Lydia Ko and Paula Creamer.
Pettersen opened play at the 10th hole Thursday with a bogey and two pars. She pulled back to even with a birdie at No. 13 and had three birdies and a bogey over Nos. 15-18 to make the turn at 2-under.
She also had a bogey to start the second nine but answered with birdies at 2 and 3. A closing string of three birdies left her alone in the lead.
Korda and Sweeney were bogey-free in shooting their 67s while Park had one bogey against seven birdies Thursday. Ricordeau was 6-under through 11 holes but went bogey-double bogey at Nos. 5 and 6 -- her 14th and 15th of the round -- to fall back. Birdies at 7 and 8 returned her close to the lead.