Home rider Vincenzo Nibali won the Tirreno-Adriatico race for the second year running after finishing 12th in today's seventh and final stage.
Britain's Chris Froome and Alberto Contador of Spain, likely contenders for the Tour de France title later in the year, finished second and third respectively.
The last 9.2-km stage, a flat ride, was won by world time trial champion Tony Martin of Germany.
"This second Tirreno win is very important not just because it is my first win of the 2013 season," said Nibali who was third behind winner Bradley Wiggins and second-placed Froome in last year's Tour de France.
"It's also important because of the riders I've managed to beat like Contador and Froome," the 28-year-old Astana rider told reporters after winning one of the highest-quality Tirreno races for several years.
"In the final time trial I had a good margin so I didn't want to take any risks on a few of the wet corners."
After losing ground to Froome on Friday and Saturday, Nibali turned the tables in spectacular style during Monday's rain-soaked short climbs and perilous descents at Port Sant'Elpidio.
"I had to make my move at exactly the right time yesterday," said the Italian. "In the Tour de France last year Sky laid down the law with a great team.
"But there weren't any stages like yesterday's or any hard, rainy days."
Second behind Martin on the final dash along the windswept Adriatic coastline was Italy's Adriano Malori. Andrey Amador of Costa Rica was third.
"It was more like a prologue than a time trial. I'd have preferred it to be longer," said Omega Pharma-Quick Step rider Martin.
"But the route wasn't too technical and I'm happy to get a win after not being able to follow the best in the mountains."