Tournament host Annika Sorenstam, meanwhile, continued to struggle with 75. She's eight shots off the lead.
No one could keep up with Gustafson in the third round.
Tied with Webb when the round began, the Swede started quickly with an eagle and two birdies on her first six holes to go four up on the Australian Hall of Famer.
Gustafson continued to build her lead, bouncing back from a double bogey on the 12th -- her first bogey in 33 holes -- with two birdies down the stretch. Na-Yeon Choi shot 68 to tie Webb (73) for second.
CHAMPIONS TOUR: In West Des Moines, Iowa, Nick Price shot 5-under-par 66 and took a one-shot lead after the second round of the Principal Charity Classic.
Price enters the final round at Glen Oaks Country Club with a 6-under 136 total. Six players, including Bobby Wadkins, Mark McNulty and Iowa native Lonnie Nielsen, are one shot back.
Joey Sindelar and Tom Purtzer both shot even-par 71s and are two shots back at 4-under. Defending champion Jay Haas, who last week won the Senior PGA Championship, shot 68 and was also at 138.
EUROPEAN TOUR: In Newport, Wales, Scott Strange maintained a three-shot lead after the third round of the Wales Open, despite battling dizzinees on the back nine. The 31-year-old Australian, who began the day with a four-stroke lead, shot 2-under-par 69 to reach 15-under for the tournament.
EUROPEAN LADIES TOUR: In Mu-nich, Germany, Michelle Wie shot 2-under-par 70 in the third round of the Ladies German Open but still fell seven strokes behind leader Amy Wang, who had a course-record 63.
CURTIS CUP: In St. Andrews, Scotland, former NCAA champion Stacy Lewis and Alison Walshe stayed perfect on the Old Course, hanging on to win the final fourball match to give the Americans a 71/2-41/2 lead over Great Britain & Ireland.
The Americans, who have won the Curtis Cup five consecutive times, need only 21/2 points today to retain the cup.
NATIONWIDE TOUR: In Glenville, Ill., Kris Blanks birdied the first five holes and ended up shooting 3-under-par 69 to share lead in the Bank of America Open.
Blanks is at 12-under 204 for three rounds at The Glen Club, along with David McKenzie (67 on Saturday) and Skip Kendall (71).