"For me, it's the most beautiful race of the season, the race of my life," said Ballerini, after securing his second Paris-Roubaix victory, having won it in 1995. Ballerini covered the 266km (160 miles) of the century old race in 6hr 57min 49sec.
The 32-year-old from Florence began his final drive 45km from the finish line and led home two Mapei team-mates by 4min 16sec. Another Italian, Andrea Tafi, came in second, followed by the Belgian Wilfried Peeters. Leon Van Bon, of the Netherlands, and the Frenchman Frederic Moncassin came home in fourth and fifth place.
Two of the favorites - Belgian Johan Museeuw and Italy's Stefano Zanini - fell on the muddy, cobblestone section running through Arenberg forest, 113km from the finish line.
Zanini came off relatively lightly, emerging with a bloody mouth after tumbling into a ditch. However, Museeuw's season could be over after he came to grief following a collision with a photographer.
Museeuw, the Belgian who won the Paris-Roubaix in 1996 - the year he took the world crown, fell on the toughest part of the cobbled sector and was taken to hospital.
"Johan will be out for a few months, possibly until October," the Mapei team director, Patrick Lefevere, said, who questioned whether such a hazardous section should be included in the race.
The Frenchman Frederic Guesdon, the winner last year, also fell in Arenberg forest.
Overall, 50km, or nearly 20 percent of the race, is runn over cobblestones, although that has been reduced as roads are repaved. Some stretches have been placed under protection as historical sites.