But the Azzurri came roaring back through winger Benvenuti who continued the form that saw him pick up five tries in last year's Heineken Cup.
Italian skipper Sergio Parisse began the move off the back of a scrum before the ball found its way to Benvenuti who beat Rory Lamont to run in from half-way, Mirco Bergamasco converting.
Dan Parks added a second penalty just before the break as the Scots took a 13-7 lead, but scrum-half Semenzato grabbed Italy's second try eight minutes after the break.
Benvenuti's kick put Scottish scrum-half Mike Blair under pressure and when the Italians turned the ball over Semenzato scrambled past Richie Vernon to bring Italy back to within a point.
But that was as close as it got for the Azzurri with Mike Blair taking advantage of Andrea Masi's delay when trying to clear, charging down the full-back for Scotland's second try.
Parks added the conversion and a further penalty as Scotland held on for a nine-point win.
Despite the defeat Benvenuti and Semenzato will both be part of the Italy squad for the World Cup, making both unavailable for the start of Treviso's RaboDirect PRO12 campaign along with ten other members of Franco Smith's side.