Annika Sorenstam, the winner of the 2002 and 2003 Kellogg-Keebler Classics, closed with a 4-under 68 to share second place at 11-under-par 205.
She was joined there by Jeong Jang (69) and Siew-Ai Lim (66). Angela Stanford and Lorena Ochoa ended one stroke further back at minus-10.
Webb, who wins her 30th LPGA Tour crown, opened with five straight pars at Stonebridge Country Club. The Australian then dropped in back-to-back birdies from the sixth.
The 29-year-old, whose last win came last September at the J.Q. Hammons Hotel Classic, birdied the par-5 ninth for the third straight round to move to minus-14.
Webb was not done. She ran in a birdie at the par-5 14th and closed out her win in fine fashion by sinking a 14-foot birdie putt at the last.
'I got my putter going good, which felt great,' said Webb, who earned $180,000 for the win. 'I didn't make too many mistakes. Everything came together this week and I really tried to trust my swing and just let it go.'
Sorenstam, trying to win her second straight tournament after winning the LPGA Corning Classic last week, began her round with nine consecutive pars. The Swede notched her first birdie at the par-4 10th. She came back with a birdie on 12 to get to minus-9.
The 33-year-old Sorenstam ran off three consecutive pars before collecting her third birdie at the 16th. She finished with a birdie at the par-5 closing hole to share second place.
'I wanted to get off to a good start and I was trying to climb the leaderboard, trying to put pressure on the leader early on,' said Sorenstam. 'It was just one of those days where it really didn't flow as much as I like it to. When you're chasing somebody by four, you need some good breaks, you need some good momentum early on so you can get going. I just didn't have that today.'
Lim, whose best finish came in 2001 when she tied for 17th at the Electrolux USA Championship, notched three birdies on both the front and back nines for a bogey-free 66.
Jang opened with a birdie at the first, but bogeyed the very next hole. She later converted back-to-back birdies from the seventh before stumbling to a bogey at the ninth.
The Korean came right back to birdie No. 10 and grabbed another birdie at the 12th. Jang faltered to her third bogey at the 16th, but managed to grab a share of second place with a birdie on the 17th.
Cristie Kerr, Yu Ping Lin and Isabelle Beisiegel shared seventh place at 9-under-par 207. Jamie Hullett, Pat Hurst, Seol An Jeon, Lorie Kane, Christina Kim, Candie Kung and Audra Burks ended one stroke further back at minus-8.