Lydia Ko, the talented 16-year-old New Zealand amateur, threatened throughout, but eventually she gave way to experience. But her time for stacking up the majors will undoubtedly come. She has already won four times playing alongside the professionals and, just last month, she retained the Canadian Open.
Pettersen closed with a 68 for 10 under par, and Ko had a 70 for eight under after the thrilling head-to-head. The winner got £315,000; Ko securing no money but huge pride in her performance.
Ko actually led on her own yesterday after almost holing out for eagle with her second shot at the opening hole, and was level with Pettersen after seven holes. But the 32-year-old Norwegian, one of the stand-outs of Europe's Solheim Cup victory in Colorado last month, birdied the seventh from 25 feet- the fist pump signalled she was very aware of the importance of the effort - and she moved two ahead after her young playing partner failed to make par at the long 13th. It was back-to-back LPGA victories for the world No.3 - she took the Safeway Classic in Oregon two weeks ago - and a 13th title on the tour.
In addition to the £315,000 cheque came the most important element - a second major title to set alongside her 2007 LPGA Championship.
"It's great to win another major and this one has definitely been well worth waiting for," said Pettersen. "I was actually really nervous coming down the stretch and even nearly played up short at the 18th (a par-four over water). But I said to my caddie I had to go for it and it worked out."
With Thursday's play having been a wash-out it had been decided on Friday to cut the event to 54 holes. Even then, it was a race against time to get things completed by dark last night.
Overnight rain caused a two-hour delay to the starting times and the odd shower during the day raised further cause for concern. Heather Daly-Donofrio was the woman in charge of tour operations for the LPGA and she admitted: "It's a miracle we got done."
The fact that they did was thanks to much hard graft and no sparing of expense. All 18 greens were put under cover on Saturday night and the hordes of greenstaff were helped by the good folks from the surrounding Evian-les-Bains community to make the course playable.
One of the problems was that the Evian Resort Course had been ploughed up and rebuilt over the past nine months. The massive disruptions to the land meant it was not draining as it had. So the hope is that when the championship returns in the same next year similar weather - ironically September is known as the "dry month" in these parts - will not cause so much disruption.
Catriona Matthew was the lone Scot in the field and never really reached full throttle. She made the cut with nothing to spare but finished with a 74 and was outside the top 60 on seven-over par. Another stand-out of Europe's Solheim Cup victory and winner of the Aberdeen Asset Management Scottish Ladies' Open at the startof the month, she will now have a short break before the Asia leg of the LPGA Tour.
Inbee Park, the South Korean who won the first three majors of the year, also had a low-key championship. Having played with Matthew for the first two rounds, she closed with a 76 for eight over par.