'I never try to plan ahead. I just play what the course gives me,' Pettersen said Saturday after opening a seven-stroke lead.
Positioning herself perfectly for a second straight victory and third in four weeks, the fourth-ranked Norwegian star birdied five of the last seven holes for a bogey-free, 9-under 63 -- the lowest round of the week.
'It's good to extend my lead,' Pettersen said. 'Tomorrow is not going to be easy. I have to shoot a low round and play aggressive.'
At 20-under 196, she topped the leaderboard for the fifth straight round and eighth in the last 11. She had two-stroke advantages the first two days at Siam Country Club, opening with rounds of 65 and 68 on the Pattaya Old Course.
English Solheim Cup teammate Laura Davies was second, a stroke ahead of American Paula Creamer. Davies and Creamer, paired together in the group ahead of Pettersen and Canadian Alena Sharp, had matching 66s. Sharp (72) was 9 under along with Australians Rachel Hetherington (68) and Katherine Hull (68).
'I have to shoot 9 or 10 under to catch up with her, which is not going to be easy,' Davies said. 'Hopefully, Suzann won't have a low round tomorrow.'
Creamer attracted a large gallery.
'I didn't expect to have so many fans,' Creamer said. 'It's good to have them come to support me and respect my golf, though it gives a bit of pressure because I want to play well before them.'
Annika Sorenstam shot her second straight 68 to get to 8 under. The 10-time major champion is making her first start since early September and eighth since returning from neck and back injuries. She won the last of 69 tour titles in September 2006.
American Stacy Prammanasudh (69) also was 8 under. She had a hole-in-one on the par-3 eighth hole. Christina Kim (71, 2 over) also aced the hole.
Defending champion Hee-Won Han, making her first start since the birth of her first child this summer, was 5 under after a 72. She won last year at Amata Spring.
Former Duke star Virada Nirapathpongporn topped the five Thai players, shooting a 70 to move into a four-way tie for 21st at 3 under. Onnarin Sattayabanphot was 2 under after a 70, and 11-year-old Ariya Jutanugarn's 74 left her 7 over.
Pettersen birdied the par-5 first for the third straight day, made another birdie on the second, then picked up two more strokes on the front nine to make the turn at 15 under -- three shots ahead of Davies.
Davies cut it to two with a birdie on the par-5 10th, but Pettersen countered with birdies on Nos. 12, 13, 15 and 17 and 18 to push her advantage to seven.
Pettersen began the run three weeks ago with a playoff victory over top-ranked Lorena Ochoa in the Longs Drugs Challenge, then won the shortened event last week in South Korea for her fourth LPGA Tour victory of the season.
Pettersen also had a chance to win two weeks ago, but slipped to fifth in the Samsung after starting the final round tied for the lead with winner Ochoa.
Sidelined for eight months in 2005 by a career-threatening ruptured disk in her back, Pettersen got off to a disappointing start this year when she blew a late three-stroke lead in the Kraft Nabisco. She rebounded to win the Michelob Ultra Open in May for her first LPGA Tour title, took the McDonald's LPGA Championship in June for her first major, then returned to Norway in August to win a European tour event