'I guess I'm really happy and a little relieved to play well today,' said Webb, who picked up $150,000 for the win. 'It's not so much winning by nine, but just that I played well enough to win.
'I guess it's just a sense of relief and I'm proud because, I mean it's not been the easiest of years for me. It just shows that all the hard work pays off and I'm really pleased.'
Dorothy Delasin also carded a Sunday 66 to move into a tie for second place. She finished along side Candie Kung (67), Tammie Green (70) and Jamie Hullett (70) at 1-under-par 209.
Webb, who went wire-to-wire for the victory, entered the final round with a three-stroke lead and was never threatened en route to her first victory since the 2002 Women's British Open.
The Australian cruised through the opening part of her round with five straight pars at Tulsa Country Club. She ran home a 40-footer for birdie at the par-3 sixth to get her round going. Webb followed that with another birdie at the eighth from 10 feet out.
However, she stumbled to her lone bogey of the day at the next when she missed the green at the par-3 ninth. That dropped her lead to three shots, the slimmest it was all day. Around the turn, Webb came right back to birdie the 10th.
'It was good to come back with a birdie there,' Webb said. 'I made a really good swing off the tee. So it was good to get back to 8-under. Then all of a sudden, we get around the 12th and I've got a six-shot lead. I was a little shocked.'
As her lead grew with no one threatening, Webb cruised to the house with four straight pars. She extended her lead even further at the 15th when she rolled in a birdie try from 12 feet out. She capped her dominating win with a six-foot birdie at par-3 17th, which she birdied all three rounds.
'It was nice to walk down the last hole with such a big lead, and not have to worry about how I played the hole,' said Webb. 'The way I played Saturday, I could have shot 3- or 4-over. Not that I would have been out of it, but it would definitely have been a lot more difficult today.'
Se Ri Pak climbed into a share of sixth place thanks to a 3-under round of 67 on Sunday. She was joined at even-par 210 by Cristie Kerr (73), Emilee Klein (70) and Jill McGill (71).
Annika Sorenstam, the 2002 champion, headed a group a 1-over-par 211. Also finishing at plus-1 were Miriam Nagl, Rachel Teske, Audra Burks and Pat Hurst.