Pettersen, who won the event last year, had a 3-under-par 69 that left her at 7-under 137 for the tournament.
Yoo Sun-young matched Pettersen's 69 and pulled into a tie for second with Carlota Ciganda, who had a 70 in the second round, at 2-under 142. Katherine Hull-Kirk (70) and Beatriz Recari (71) are tied for fourth at 143.
They are the only players under par for the tournament, played in stiff winds.
"The wind got stronger and stronger and it's definitely not easy out there. The wind and the conditions test every aspect of the game," Pettersen said. "Standing over putts, you feel the wind on the body. It's a mental test out there but it's a fun challenge."
She beat the wind at the second hole, using a wedge on the 133-yard, par 3 for her third LPGA ace.
"I called the shot, I hit it exactly how I wanted and was fortunate enough that I had a good break," she said. "It was a very good shot. It's nice to get a hole-in-one when you actually call the shot in advance and then pull the trigger."
Petersen was 3-under for nine holes after a birdie at No. 9 and played the back nine even with a bogey at 14 and a closing birdie.
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