Pettersen, the event's defending champion, had three bogeys in the first five holes of the third round and settled for a 1-over-par 73. She's at 6-under 210 for the tournament.
Azahara Munoz carded a 3-under 69 and is tied with Carlota Ciganda and Yoo Sun-young, who each were even 72 Saturday, for second at 2-under.
Caroline Hedwall, also with a 72 in the third round, and Beatriz Recari, who was 1-over Saturday, are tied for fifth at even-par 216.
Those are the only players at par or better.
Pettersen led by five strokes after Friday's second round but eroded her lead with bogeys at 2, 4 and 5 to open the day. That pulled Yoo to as close as one stroke of the lead before Pettersen gave herself some room with birdies at 8 and 13. She had a fourth bogey at 17 but closed with a birdie.
Munoz had a third-hole bogey but was 4-under the rest of the way Saturday. Yoo mixed two birdies and two bogeys for her 72 while Ciganda had a third-hole double bogey along with one bogey and three birdies.
Swim Week Miami Beach 2014 [PHOTOS]