Johnson had not won on the European tour since 1992, nor anywhere since winning back-to-back tournaments in America in April 1993. A final round 70 increased her four-shot advantage from the beginning of the day by a further stroke, with Australia's Anne-Marie Knight and Sweden's Pernilla Sterner tying for second place at nine under.
Despite a bogey at the first hole, Johnson responded with an eagle at the next, holing from 15 feet, and never looked back. "It has been a long time since my last win, so I am very, very happy," Johnson, 30, from Bristol, said. "I felt fairly in control round about the turn. Nobody made a run early on which helped. I didn't hit too many good shots coming in, but they all ended up somewhere around the green."
Though a team victory against the Americans at St Pierre is the main priority, Johnson is determined to do something about a record of one win, one half, and seven losses in three previous matches. "If the team wins, I couldn't give a monkey's how many points I get, but I haven't contributed enough and I feel I have let the team down. I have got the most appalling record."
Johnson had trailed Laura Davies by three strokes at the half-way stage, but it was a weekend the world No 1 will want to forget. After collecting 13 birdies over the first two days, including a course record 63 on Friday, Davies could manage no more than three on the last two days, all of them yesterday, as she closed with rounds of 76 and 75.
On a course measuring only 5,954 yards, Davies's advantage in the massive distances she can hit the ball proved no help. Only once, in eight attempts, did she birdie a par-5 hole on the weekend.
On Saturday she claimed to be playing as well as the day before, but her long game put her in too much trouble for her faltering putting to come to the rescue. It was on the greens, again, yesterday, where a potential challenge was stymied. "I should have been six under for the front nine," Davies said. "I missed six putts from inside three feet. It's heartbreaking when that happens."
Davies went to the turn in 35 and came home in 40, but still finished in seventh place. Dale Reid, the third member of the European Solheim Cup team in attendance, closed with a 70 to finish in fifth place, her best finish of the season. That, above anything else, may be the best news for captain Mickey Walker, who made Reid the last of her wild card selections.
Scores, Digest, page 23