Fraser missed a short, par-saving putt on the fourth playoff hole while Willett recovered from overshooting the green on his approach shot, ultimately corralling a par for the championship at Golf Club Gut Larchenhof.
Britain's Willett triumphed for the first time in 106 career tour starts, shaking off rainy conditions to win the lengthy duel with his Australian opponent.
He had forced the playoff by parring his final three holes, finishing with a 1-over 73 to end regulation knotted with Fraser at 11-under 277.
The Australian, meanwhile, stumbled to a bogey the final hole of regulation, carding a 1-under 71.
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