Pettersen's bogey-free 65 got her to 10-under 134 after 36 holes. Park, the first-round leader, had two bogeys in a 3-under 69 in the second round.
Defending champion and world No. 1 Yani Tseng shot 69 and is tied for third with Catriona Matthew, who opened her round with three birdies and shot 66. Tseng and Matthew are at 8-under for the tournament. Alison Walshe, with a 67, is alone in fifth at 6-under 138.
Park took the first-round lead with a bogey-free 65 Thursday but suffered her first bogey at No. 4 Friday. However, she had four consecutive birdies over Nos. 6-9. After seven pars, she took a 5 at the par-4 17th before closing with a birdie.
Pettersen used birdies at 4 and 9 to make the turn at 2-under but had five birdies on the second nine in earning a share of first.