Petacchi has nine stage wins in the Tour of Spain in total

It was his second win in the 2004 La Vuelta following his victory in Sunday's second stage.

T-Mobile's Erik Zabel was second, with Oscar Freire of the Rabobank team third on the 167.5km (104-mile) stage between Soria and Zaragoza.

Luxembourg's Benoit Joachim of US Postal retained the overall lead.

It is the second year in succession that Petacchi has triumphed in a bunch sprint.

"I knew it was going to be close because of the winds which made it a lot harder for a team throughout the stage," said the Fassa Bortolo rider, who amassed nine stage wins in this year's Giro d'Italia.

Meanwhile, leading contender American Tyler Hamilton went down in a four-man pile up at 112 km but was able to continue.

"He has grazes in his right side, elbow, hip and leg but basically he was OK," official race doctor Juan Maria Irigoyen said.

In a separate incident, a British man is due to be charged by Spanish police after hurling a rock into the peloton during stage three.

The rock struck the bike of Kazakh rider Alexandre Vinokourov, third in the 2003 Tour de France, and reportedly destroyed one of his wheels.

Fourth stage result:
1. Alessandro Petacchi (Italy) Fassa Bortolo 4 hour 23 minutes 01 seconds
2. Erik Zabel (Germany) T-Mobile
3. Oscar Freire (Spain) Rabobank
4. Stuart O'Grady (Australia) Cofidis
5. Angelo Furlan (Italy) Alessio-Bianchi
6. Giosue Bonomi (Italy) Saeco
7. Miguel A. M. Perdiguero (Spain) Saunier Duval
8. Pedro Horrillo (Spain) Quick Step-Davitamon
9. Arnaud Coyot (France) Cofidis
10. Luca Paolini (Italy) Quick Step-Davitamon, all same time