Seeking her second straight victory and third in four weeks, Pettersen missed an opportunity to take a much bigger first-round lead, playing the final seven holes in 1 over after birdieing eight of the first 11.
'These greens, you just have to attack where you can attack and, if you can't, then you have to play for the big center part,' Pettersen said. 'The greens are tough because the runoffs are so severe.'
The Norwegian star won last week in South Korea in cold and windy conditions.
'It's very warm, but the breeze makes it quite nice,' Pettersen said. 'So, I just tried to go out there and take what the course gave me. It's like last week, you could stand and talk about the shot and then, when it's your turn, the wind's turned.'
She shared attention with Thai amateur Ariya Jutanugarn, at 11 years, 11 months, 2 days the youngest qualifier to play an LPGA Tour event.
Jutanugarn, 10 strokes back after a 3-over 75, broke Michelle Wie's mark of 12 years, 4 months, 14 days set in the 2002 Takefuji Classic. Beverly Klass holds the overall record, playing a 1967 event in Dallas at 10 years, 6 months, 3 days.
Jutanugarn's 13-year-old sister, Moriya, served as her caddie.
Sharp, winless in two full seasons on the tour, had six birdies and a bogey in her 67 on the Pattaya Old Course at Siam Country Club.
'Last week, you had to try to stay warm and, this week, you're sweating to death,' Sharp said. 'Mentally, I think, I knew last week, with the cold weather, a lot of girls wouldn't play very well. It's just harder in the cold. It's so much easier in the warmth. Now, you're looking for shade out here this week.'
Angela Park and Katherine Hull shot 68s.
'I didn't hit it great, but I didn't miss it badly, either,' said Hull, from Australia. 'I made a couple good putts and it all adds up. ... I'm just trying to get my timing back with my golf swing. It's still a little off, but it's not rocket science. I just try to hit the fairway, hit the green.'
Park three-putted the 18th for a bogey, missing from a foot.
'A little careless on the last hole,' Park said, 'but I played well throughout the whole day and I don't think I should let one putt put me down.
Annika Sorenstam, winless since September 2006, was seven shots behind at 72 along with Paula Creamer, Brittany Lincicome and Thai star Virada Nirapathpongporn.
Defending champion Hee-Won Han, making her first start since the birth of her first child this summer, topped a group at 69. Last year at Amata Spring, Han beat Diana D'Alessio by five strokes for her sixth LPGA Tour victory.
Kraft Nabisco winner Morgan Pressel and Japanese star Ai Miyazato struggled. Pressel shot a 75, and Miyazato's 79 left her tied for 56th in the 60-player field.
Pettersen birdied the first three holes and ran off three more on Nos. 6-8, hitting wedges within 4 feet for her first five birdies and holing a 20-footer for the sixth.
After parring No. 9 for a front-nine 30, she reached 8 under with two more short birdie putts on 10 and 11. She dropped strokes with three-putt bogeys on 13 and 16, but hit a wedge to 4 feet for a birdie on 18.
'We had a lot of short irons into the greens, but you still have to hold them,' Pettersen said. 'It's hard to adjust how much they're going to bounce and stuff. But, I'm playing great. I hit 16, 17 greens and had a lot of short putts for birdie.'
Sidelined for eight months in 2005 by a career-threatening ruptured disk in her back, the three-time Solheim Cup player has already had a career year.
After blowing a late three-stroke lead in the Kraft Nabisco, she rebounded to win the Michelob Ultra Open in May for her first LPGA Tour victory. Then in June at Bulle Rock, she took the McDonald's LPGA Championship for her first major.
She also won the Ladies European Tour's SAS Masters in August in Norway, and beat top-ranked Lorena Ochoa three weeks ago in a playoff in the Longs Drugs Challenge. In Pettersen's lone loss in the past three weeks, she was fifth in the Samsung after sharing the third-round lead with winner Ochoa.