Having taken a four-stroke lead into the final round, US Masters champion Scott stumbled with a double-bogey on the par-three 14th hole to concede a two-stroke lead to world number eight Kuchar on a gusty day at Royal Melbourne.
But the 35-year-old American's challenge crumbled on his final few holes with a bogey on the par-four 16th and a double-bogey on the par-four 18th to gift Scott a two-stroke lead heading to the last hole.
Roared on by a huge gallery, the home hero Scott tapped in a three-foot par putt to complete an even-par round of 71 for a 14-under total of 270.