"I just tried to make a good swing and blocked it left,'' Mickelson said. "I hit a good shot out of the swamp, but I hit the third shot way too hard.''
Mickelson, winless on the PGA European Tour, also bogeyed the 14th and 16th holes in regulation, but bounced back with birdies on 15 and 17.
Mickelson, whose only victory abroad was in the 1993 Perrier Open in Paris, a second-tier event, began the day with a one-stroke lead. He stayed in front until the 14th hole, when his bogey and Havret's birdie left them tied.
"When Greg plays solid like that, not only does he deserve to win, but he makes himself very tough to beat,'' Mickelson said.
Two-time Loch Lomond winner Ernie Els made a 40-foot birdie putt on 18 to finish third, a stroke out of the playoff. Luke Donald (64), Richard Sterne (64), Pelle Edberg (66) and Louis Oosthuizen (68) tied for fourth at 11 under.