Cavendish made the most of the last stage designed for sprinters before the race reaches the Pyrenees to claim his 18th stage win at the Tour, his third in this year's race. He won in 3 hours, 46 minutes, 7 seconds.
"It's incredible to have the green jersey, it's the most beautiful jersey in the world," said Cavendish, who benefited from a perfect lead-out by his HTC-Highroad teammate Mark Renshaw to prevail with a bike length.
"I'm super happy. I hope I get to keep the green jersey this year. We've been fighting for it all along. All the intermediate sprints we've gone for, the finishes we've gone for ... and 15 points is a narrow margin and we'll keep fighting."
Cavendish, who took the jersey from Philippe Gilbert of Belgium, now leads Jose Joaquin Rojas by 16 points. He will have two more opportunities to win stages before the race ends on the Champs Elysees on July 24.
"There are two more bunch sprints in this year's race, one in Montpellier and the other in Paris and I want to try to win both of them."
French rider Thomas Voeckler kept the race leader's yellow jersey after the 167.5km trek from Blaye-les-Mines to Lavaur. Voeckler finished 75th in the stage but with the same time as the winner.
Despite his impressive tally of stage wins at the Grande Boucle, the coveted sprint champion's jersey has so far eluded the 26-year-old Cavendish.
He was second last year, 11 points behind Alessandro Petacchi of Italy, and second by 10 points to two-time sprint champion Thor Hushovd in 2009. Cavendish pulled out before the Alpine stages in 2008 to conserve energy for the Olympic Games.
Cavendish claimed revenge for his loss to Greipel in Tuesday's stage, when his former teammate surged ahead at the finish to claim his first win on the Tour.
"I said yesterday that it could have been four or five wins by now actually but I've got no regrets," Cavendish said. "The first (sprint) stage when Tyler (Farrar) won was one for me, and yesterday when Greipel beat me, I could have won there, too. Yesterday, I didn't kick. I kind of rolled before kicking, so I made sure I kicked today."
Voeckler said he is now expecting to lose his yellow jersey during Thursday's 12th stage, which takes the riders on the first of a three-day trek across the Pyrenees with a punishing 211km ride over the legendary col du Tourmalet and finishing on top of Luz-Ardiden.
The stage is likely to be a key moment of the race. It also features a new climb, the Hourquette d'Ancizan, a 9.9km ascent with an average gradient of 7.5 percent.
"The Schleck brothers have a strong team, which might be more united than Contador's one," Voeckler said. "Evans looks in great shape and his teammates are doing an amazing job for him. They all be there tomorrow."
With their minds already on the big mountain battle to come, three-time champion Contador and his rivals stayed comfortably in the pack and didn't take any risks.
Contador, who has been hampered by crashes this year, trails Cadel Evans of Australia and Andy Schleck of Luxembourg by 1:41 and 1:30, respectively, before visiting his favorite playground.
The stage came alive after 13km when six breakaway riders - Ruben Perez Moreno, Tristan Valentin, Jimmy Engoulvent, Mickael Delage, Lars Boom and Andriy Grivko - went away under a slight rain.
Although none of the escapees were a threat to the Tour contenders or to Voeckler's overall lead, the peloton kept them on a leash and the group had a maximum lead of 4 minutes, 20 seconds after 43km.
Being pushed along by a strong tail wind, the bunch started the chase before the intermediate sprint halfway through the stage, where Cavendish took seventh place ahead of Rojas to earn nine more points.
HTC-Highroad manager Bob Stapleton said intermediate sprints tired out Cavendish this year after race organisers changed the rules. There is only one intermediate sprint on each stage, with 20 points available to the rider who wins - as opposed to six points in previous years when there were more intermediate sprints.
"They've been full on sprints and they've been exhausting, that does consume a lot of resources," Stapleton said. "It probably met the goal of the organisers, because they're exciting and they're good television."
HTC-Highroad riders, joined by Omega-Pharma-Lotto and Garmin-Cervelo cyclists, then shared the workload at the front of the peloton to set a faster tempo as the escapees saw their lead drop to 1:34 at the top of the small Puylaurens climb, with 32km to go.
The breakaway worked efficiently, with all riders taking turns in front, until Boom attacked alone 4km from the line, moments before his companions were reined in.
Boom was caught with 2km to go.
