Gustafson was 1-under for her round when she knocked a 200-yard 4-iron to three feet to set up an eagle at the par-5 16th. After a 9-iron approach to the par-4 17th left her with a short putt for birdie, Gustafson managed to cap her round with a 20-foot eagle putt at the closing par-5.
'It was really nice. That's probably my best ever finish to a tournament,' said Gustafson, who carded the day's best round of 6- under 66 in windy conditions for a three-day total of 11-under-par 205. 'The putts were just short ones on 16 and 17, but it was nice to finish so strong on 18.'
The 27-year-old Gustafson was three shots back at the start of the day and made it to 8-under par with three birdies before the turn. Although she stumbled a bit with bogeys at the 11th and 15th, Gustafson quickly leaped to the top of the leaderboard with her sensational finish.
When Gustafson is paired with Webb on Sunday, it will mark the second time this season that the two have gone head-to-head in a final round. Gustafson got the better of the Aussie back in January, posting a three-shot victory over the top-ranked Webb at the LPGA's Memorial of Naples event.
'It's nice to have a four-shot lead over [Webb],' Gustafson said. 'That means she's going to have to play very good to beat me tomorrow.'
Gustafson, who broke through on the LPGA Tour last year with a triumph at the Chick-fil-A Charity Championship, was the No. 1 player on the 2000 Evian Ladies European Tour with wins in the Italian and Irish Opens. She went on to capture the Women's British Open, an event that is co-sanctioned by the European and LPGA tours.
The Swede also posted a 2-1-1 record to help Europe defeat the U.S. in the 2000 Solheim Cup.
Webb opened with a bogey on Saturday but made four birdies over a seven-hole stretch midround to grab a share of the lead with Gustafson at 7-under. Webb then had the lead to herself when Gustafson bogeyed 15, only to watch Gustafson pull away at the end with two eagles and a birdie.
'I felt like I hit the ball pretty well for the conditions,' said Webb, who finished with a 3-under 69 to get to 7-under 209. 'It was tough out there and you really had to grind it out. The conditions got a little easier for us in the last few holes, but before that it was really tough to try and judge which way the wind came.'
The 26-year-old Webb won her fourth consecutive Australian Ladies Masters title at the Royal Pines Resort last week.
Crafter, the winner of this event in 1997, turned in a 2-under 70 for a share of second place with Webb, while Munt followed up rounds of 65-71 with a 78 on Saturday that featured four bogeys and two double-bogeys.
Tied for fourth with Munt at 2-under 214 are Becky Morgan (72) and Corinne Dibnah (76).
England's Laura Davies, five strokes back at the start of the day, struggled to a 78 and slipped 14 shots off the pace to 3-over par.