After an expert lead out by team-mate Mark Renshaw, the HTC-Highroad rider timed his sprint to perfection, latching on to Petacchi's wheel before blistering to an effortless win in the 159-kilometre stage in the Abruzzo region.
Knowing he was beaten, Petacchi (Lampre) took his foot off the gas to allow Spaniard Ventoso (Movistar) to take second place.
Cavendish was quick to praise his team-mates after winning his first stage of what has proved to be a very testing race for pure sprinters.
"There are only three proper sprints in this Giro and to be fair I thought the win would come in the first sprint and not as late as now," Cavendish told Eurosport at the finish.
"But the team stayed hungry and they all did an incredible job. We'll target another one in Ravenna," the 25-year-old added, referring to Thursday's pancake-flat stage 12.
The victory will be all the sweeter for Cavendish following claims made by Ventoso that the Briton should have been disqualified from the race for holding on to a team car during the gruelling ascent of Mount Etna on Sunday.
Cavendish finished stage 9 almost half an hour behind stage winner Alberto Contador - just 25 seconds within the cut-off time.
But Cavendish was quick to rubbish the Spaniard's accusation, stressing his HTC team always practised fair play.
"I know what he (Ventoso) said," Cavendish told Eurosport. "If I stop for a p*** or a wheel change I have the cameras in my face - and it's always like that with me. Our team is currently leading the fair play standings. I know what I do and my team do too."
Stage 10 was played out under stormy skies alongside the Adriatic coast. A three-man breakaway made up of Fumiyuki Beppu (RadioShack), Pierre Cazaux (Euskaltel-Euskadi) and Yuriy Krivtsov (AG2R La Mondiale) quickly formed after a few kilometres of racing, building up a lead of six minutes.
Japanese rider Beppu, as well as his RadioShack team-mates, sported a sticker on his bike with the words "I ride for Wouter Weylandt" next to the 108 starting number of the late Belgian rider, who tragically died in a fall during stage three of the race.
The three escapees were reeled in with 12km left to ride, setting the scene for a bunch sprint. With straightforward flat finishes something of a rarity in the 94th edition of the Giro, the HTC team of Cavendish were never going to let the opportunity pass to give their man his best shot of victory.
Cavendish duly delivered to win the sixth Giro stage of his career. Contador (Saxo Bank-Sunguard) retained his overall leader's pink jersey.
Wednesday's undulating 142km stage 11 from Tortoreto to Castelfidardo includes four fourth category climbs and a handful of other minor hills, which should prove ideal terrain for a breakaway.
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