Petacchi stormed to victory as Cavendish (left, in distance) faded
Alessandro Petacchi won a thrilling sprint finish to take the fourth stage of the Tour de France but Mark Cavendish's challenge faded away.
Italian Lampre rider Petacchi seized the initiative after Cavendish dropped out of the sprint to claim victory in the 153km stage from Cambrai to Reims.
Fabian Cancellara retained the yellow jersey after crossing in the main pack.
Isle of Man sprinter Cavendish's 12th-place finish cast doubt over his chances of winning the green jersey.
The 25-year-old HTC-Columbia rider, who won six stages in last year's Tour, is now well adrift of green jersey leader Thor Hushovd (Cervelo).
The flat fourth stage was significantly more accommodating for riders following three days of tough cycling in slick conditions and over cobblestones which saw a series of crashes.
Frenchman Dmitri Champion attacked after 1.5km and was quickly joined by Francis De Greef, Nicolas Vogondy, Iban Mayoz and Inaki Isasi. The quintet stayed clear until the final few kilometres when the field finally came back together to contest the bunch sprint.
Cavendish was perfectly positioned to make up for crashing in Sunday's sprint but after good work from his team-mates, he sat up short of the line as Petacchi stormed to victory just ahead of Julian Dean (Garmin-Transitions) and Team Sky's Edvald Boasson Hagen.
The only thing we missed today was Cav's sprint legs from last year
Sprint legend Erik Zabel
The 36-year-old Petacchi also won Sunday's first stage into Brussels in his first Tour since 2004, the year after claiming a hat-trick of sprint victories.
"I'm not like a little old man, as some have said. This win is really important for me and for the team," said Petacchi, who played down claims he only won the opening stage because a crash took out many rivals, including Cavendish.
"I've come here to win stages and I've shown twice that I'm not here to make up the numbers.
"In the over 200 sprints I've done I've learned a thing or two. But today I have to say thanks to my team, they really anticipated things despite the fact they don't have a lot of experience trying to set up sprints."
Welshman Geraint Thomas finished among the pack in 19th and as a result retains second place in the overall standings and keeps the young riders' white jersey.
Defending champion Alberto Contador remains in ninth overall after finishing 32nd, with last year's runner-up Andy Schleck sixth overall after crossing in 58th.
THOUGHT OF THE DAY
You've got to start to wonder if Cavendish has the legs and the mental capacity to bounce back and take a stage win at the Tour this year. He looked well beaten tactically and physically by the veteran Alessandro Petacchi in Reims
BBC 5 live co-commentator Graeme Jones
Seven-time champion Lance Armstrong, whose progress was hampered in stage three by a flat tyre which cost him significant time and saw him plummet from fifth in the general standings to 18th, crossed 36th in Reims.
Cavendish vented his frustration by hurling his bike to the ground at the team bus and later was at a loss to explain why his challenge had faded.
"I felt really good during the stage," said Cavendish. "I feel sorry for my team-mates who rode unbelievably and I just didn't finish it off at the end."
"We're really motivated as a team and I'm going to go out there on Thursday and give it hundred percent again. Congratulations to Alessandro Petacchi for another great stage win."
And Cavendish's lead-out man Mark Renshaw of Australia had words of comfort for the Manxman.
"It has not gone to plan yet, but I am sure Mark will win a stage. We don't have it as easy as we did last year, but we will win a stage."
HTC-Columbia consultant Erik Zabel, a six-time winner of the Tour's points classification's green jersey, added: "The team did a perfect job today.
"The only thing we missed today was Cav's sprint legs from last year."
Petacchi offered his rival some words of comfort: "He is a great sprinter. I don't think he's got things to learn from me, or anybody else.
"He won six stages last year, so he knows perfectly how to sprint. But that's sprinting. I've won twice here, but that doesn't mean I'm faster than him, or he's faster than me. Each sprint is different."
Stage five travels 187.5km from Epernay to Montargis on Thursday.
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