The 25-year-old had an eagle and three birdies in the last eight holes to finish the Grand Final in Italy in joint fifth place and climb from 28th to 20th on the money list.
The top 21 on the circuit earned cards and the player to suffer because of Benson's burst was 40-year-old Scot Raymond Russell.
He went into the week in 22nd spot just £13 behind Daniel Vancsik and although he overtook the Argentinian by finishing joint 14th, he needed one birdie in the closing three holes to get back on Tour.
Instead he finished £128 behind England's Daniel Brooks, who breathed a huge sigh of relief after finishing joint last in the event and 21st on the money list.
Victory at San Domenico went to Norwegian Espen Kofstad and that also made the 25-year-old the Order of Merit number one.
The biggest move up the rankings came from England's James Busby. He only just qualified for the Grand Final, but coming joint second swept him from 45th to 16th in the standings.
After holing for par on the 18th to complete the most important 66 of his life, the 30-year-old told the European Tour website: "That putt just summed up how I was feeling for the entire back nine - absolutely petrified.
"I couldn't really feel anything. It's the stuff of dreams really - up until today I was thinking about preparing for the qualifying school."