The victory was sweet for world No. 2 Webb, who last week was denied a fifth straight win in the Australian Ladies Masters after losing a four-hole playoff to the top-ranked Annika Sorenstam.
'It feels great to win,' said Webb, also a winner at Yarra Yarra in 2000. 'To lose two playoffs would have been disappointing, so I'm glad I won this week.'
She had to hold off the 20-year-old Pettersen, the co-leader with Webb after the second and third rounds.
Pettersen missed a 20-foot eagle putt at the par-5 18th to win the event in regulation, but birdied to match Webb's final-round 69. The pair finished 72 holes tied at 10-under-par 278, a full eight shots ahead of Australia's Michelle Ellis and Becky Morgan of Wales.
At the 18th in the playoff, Webb managed to reach the green in two while Pettersen's second shot landed in a deep greenside bunker. After Pettersen hit out of the sand to 20 feet, Webb boldly rolled her eagle attempt eight feet past the hole.
Pettersen missed her birdie putt, and Webb sank hers to secure the victory in her home country.
'Hats off to Suzann, she played really well today. She hung in there and made some great birdies coming down the stretch,' said Webb, 27, a native of Ayr, in Queensland. 'I gave myself a couple of opportunities, but couldn't make them. But I made a few putts before that, so I can't complain, and I was obviously very happy to make that last putt in the playoff.'
Defending champion Sophie Gustafson of Sweden finished alone in fifth place at 1-under 287.