"It was a very long sprint over cobblestones. It was one of the best sprints of my career," Petacchi said.
Robert Forster, a German with the Gerolsteiner team, was second. Ariel Maximilian Richeze, an Argentine with Panaria, was third, and Robbie McEwen of Australia was fourth.
After his Milram team set him up perfectly, Petacchi was passed by McEwen and Paolo Bettini in the final metres of Sunday's second stage to attract criticism that he wasn't as fast as he used to be.
Monday's victory was the 20th Giro stage win of Petacchi's career. He won six stages in 2003, nine in 2004 and four in 2005. He fell and withdrew with a broken knee cap in the third stage last year.
"I said before the Giro that a victory would be like winning my first (ever) stage. I suffered a lot after the injury," a tearful Petacchi said.
"I had a lot of doubts about whether I would return to my top level,"
Gasparotto, of the Liquigas team, regained the overall lead by placing
eighth in the sprint finish.
"We decided this morning that I would not take part in the sprint," said
Di Luca, who crossed 82nd.
Several riders were involved in a crash shortly before the finish for the
second straight day.
Race favorite Damiano Cunego fell on his right hip, but quickly got back
up. Two-time champion Gilberto Simoni was able to stop short before falling.
Thor Hushovd, a Norwegian with Credit Agricole, was also among those who fell.
Five riders formed a breakaway at the start of the stage and held as much as a seven-minute advantage over the main pack after about 75 kilometers.
The two remaining riders, Mikhail Ignatiev, a Russian with the Tinkoff
team, and Giovanni Visconti of Quick Step, were caught by the main group with four kilometers to go.
Quick Step rider Andrea Tonti, who was hurt in Sunday's crash, did not
start. Adam Hansen, an Australian with T-Mobile, also did not start.
AnotherAustralian, Graeme Brown with Rabobank, withdrew with 38 kilometres remaining in the stage.
Tuesday is a rest day as the race heads to Salerno and mainland Italy for the fourth stage on Wednesday, a 153-kilometre leg that ends with a climb to Montevergine di Mercogliano, where Cunego won en route to the 2004 title.