Pettersen fired a 5-under-par 67, as did Webb, on an overcast day at Bulle Rock and finished at 14-under 274.
Pettersen, who used a putter given to her by one of her partners in Tuesday's Pro-Am, exuded confidence the entire way and did not have any flashbacks to her Kraft meltdown.
"No, because I felt different," said Pettersen, 26, a native of Norway in her fourth season on the LPGA Tour. "I wasn't even close to being in those emotions that I was back then. Now, I finally proved to all of you that I can actually put it all together and take a major."
Eighteen-year-old rookie Na On Min, who began the day with a 1-stroke lead, staggered to three straight bogeys on the first nine, then posted four consecutive birdies on the second nine for a 70 that gave her third place at 276.
Morgan Pressel, who was 3 shots off the lead when play started in trying to go 2 for 2 in 2007 majors, closed with a 73 and finished 14th at 282.
Pettersen grabbed the lead for good at the seventh hole in the middle of Min's struggles. She reached the par-5 eighth in 2 and two-putted for birdie, but bogeyed the ninth to turn at 10 under, a shot ahead of Webb.
Pettersen got the lost stroke back with a birdie at the 10th and picked up birdies at 13 and 15. The big blow came at the par-3 17th, where she hit a 7-iron to within 15 feet and sank the putt.
When Webb made birdie ahead of her at 18, pumping her fist so violently that she nearly lost her balance, Pettersen needed a par to win. She drove in the center of the fairway, hit her approach to 35 feet, and nestled the birdie try to a few inches.
"I asked my caddie if [Webb made] a birdie, because the roar was so big, and he said yes," said Pettersen, who hit 16 greens in her round. "I think I would have played the same way even if she had not made that birdie. My goal was to hit the middle of the green and have two putts to win."
Webb, a seven-time major champion, came close to winning here for the second straight year. She lost a playoff to Se Ri Pak in 2006 after Pak put her approach shot inches from the cup. She kept the heat on Pettersen with birdie putts of 15 feet at 17 and 25 feet at 18, but had to settle for runner-up honors once again.
"I guess in the back of my mind, I knew what had happened to her at the Kraft and I knew I needed to keep putting pressure on her," Webb said. ". . . I knew if I stayed close, I would have a chance. But she executed very well down the stretch, and she should be proud of herself."
Notes. Annika Sorenstam, a three-time champion in this event, posted a 71 - her third sub-par round of the week - and tied for 15th at 283. . . . Angela Park, 18, extended her streak of consecutive holes without a bogey to 38 before her 5 at the par-4 ninth yesterday. She wound up fifth with a 279 total.
Contact staff writer Joe Juliano at 215-854-4494 or firstname.lastname@example.org.