Strong wind gusts made for tricky approach shots and putts, and Inkster's relatively bad score a day after shooting a 64 only cost her one stroke of what had been a three-shot lead. She tied Annika Sorenstam's 54-hole tournament record of 16-under 200.
Laura Diaz shot a 68 and Dorothy Delasin had a 69 to remain two shots behind the 41-year-old Inkster, the 1999 Tucson winner.
Sorenstam, the winner the last two years, made a strong charge to get into position for a run at her third title. The former University of Arizona star birdied six of the first 12 holes and finished with a 67, tied with Mi Hyun Kim (66) and Nancy Scranton (72) at 205.
The seven-player group at 206 included 1988 Tucson winner Laura Davies (70) and amateur Lorena Ochoa of Mexico, a sophomore at Arizona, who carded a 69.
Karrie Webb, trying to regain the form that made her the LPGA Tour's player of the year in 1999 and 2000, shot 70 to finish seven shots off the pace with 13 players in front and 18 holes to go.
Sorenstam won last year by six shots over Michelle McGann, Diaz, Dottie Pepper and Se Ri Pak at 23-under, another tournament record.
Neither Diaz nor Delasin has won on the tour, a sharp contrast to Inkster's 26 victories and LPGA Hall of Fame membership. She has held onto the lead and won 12 of the 23 times she took one into the final round.
Inkster also has a history of playing well on the 6,222-yard Randolph Park North municipal course, where three of the last six holes are par-5s.
In her last 10 appearances in Tucson, Inkster has finished no lower than seventh five times and been out of the top 25 just once. She was third in 2000 and tied for seventh last year.
But she played maintenance-level golf most of this round, making 10 straight pars before she bogeyed the 11th hole, a 187-yard par-3, for the second time in three days.
Inkster used a 5-iron off the tee and came up short, chipped up and two-putted from 4 feet for the bogey.
Diaz, who started four shots back, caught up at 14 under with a birdie -- her fifth of the round -- on the 11th, and was in the 12th fairway when she got sole possession of the lead after Inkster's problems back on the green.
But Inkster came back quickly by eagling the 13th hole, a friendly, 470-yard par-5 which she birdied the first two rounds. She slammed a 5-wood onto the green 15 feet from the pin and rolled in her first par-cutting putt.
After Delasin and Diaz both parred No. 18, Inkster opened room on her pursuers with a finishing birdie when she two-putted from about 20 feet.
Full-field scores from the Welch's/Circle K Championship