The main pack was split into two groups when riders went down with less than two kilometres to go and only about ten to 15 riders were left in front to contest the sprint.
Cavendish, who rides for the Omega Pharma-Quick Step team, finished the the 81-mile stage in two hours, 58 minutes, 38 seconds on the circuit in central Naples, which featured a long, flat finishing straight ideal for sprinting.
Cavendish has now won a combined 37 stages at the Giro, Tour de France and Vuelta a Espana – cycling’s three Grand Tours.
Elia Viviani, an Italian with Cannondale, crossed second, and Nacer Bouhanni, a Frenchman with Francaise Des Jeux, was third.
Overall favorites Bradley Wiggins and Vincenzo Nibali, along with defending champion Ryder Hesjedal, finished safely in the main pack.
Among those involved in the crash was Scotland’s David Millar, who later tweeted: “I love crashing the first day of a Grand Tour: glute & shoulder bruised to hell, bike broken. Congrats Mark Cavendish, delivers as usual.”
It was the 11th Giro stage win of Cavendish’s career and his 98th victory overall. He’ll wear the overall leader’s pink jersey in today’s second stage, a team time trial on the nearby island of Ischia.
It will mark the fourth time Cavendish wears the pink jersey. He wore it for two days in 2009 when his former team Columbia won the opening team time trial and for one day in 2011 after a stage win.
“I’ve worn it before at the start but that was thanks to my team,” Cavendish said. “I really wanted to win this here in Napoli. Now I want to go for a pizza.”
The course featured two mild climbs in the Posillipo neighborhood and several loops down the finishing straight alongside the bay. On a warm spring day, fans came out en masse to watch the race.
Some even brought their dogs and one of them nearly brought down some riders on a sharp corner after slipping under the barriers lining the road. With the roads narrow in areas and stretches of cobblestones, there were several crashes. Among the other riders who hit the asphalt were Laurent Pichon of France, Matteo Rabottini of Italy and Miguel Minguez Ayala of Spain.
There were a couple of groups of early breakaway riders and the last man caught by the main pack was Cameron Wurf, an Australian with Cannondale, with about 12 miles to go.
Cavendish’s Belgian Omega team had led the chase.
Today’s stage is a 10.8-mile team time trial from Ischia to Forio.