Pettersen, who opened the day nine strokes off the lead, fired a 7-under 64 Sunday and defeated Choi Na-yeon on the first hole of a sudden-death playoff in winning the Safeway Classic.
It was her eighth LPGA title in her career and second this year. She won the Sybase Match Play Championship in May.
Pettersen moves into the No. 2 spot in the world rankings with a ranking points average of 12.53. Yani Tseng remains solidly No. 1 with an average of 15.54.
Cristie Kerr, who tied for 40th at the Safeway Classic, slips to third with an average of 11.18 while Jiyai Shin (9.02) is fourth and Choi (8.74) keeps the No. 5 spot.
Ahn Sun-ju (8.14) is sixth ahead of Ai Miyazato (7.64) and Paula Creamer (7.37). Stacy Lewis (6.41) tied for eighth in last week's tournament and was able to pass Karrie Webb (6.35) for 10th in the rankings.