The top overall standings didn’t change as defending champion Cadel Evans, of Australia, and fellow title contender Bradley Wiggins trailed close behind in the pack after the 129-mile ride from Vise to Tournai.
Cavendish collected his 21st Tour stage victory and proved he remains the rider to beat in Tour sprints.
The 27-year-old from the Isle of Man has been left largely to fend for himself this year because his Sky team is focusing on helping Wiggins become Britain’s first Tour winner.
“It’s quite nice. I came into this sprint day with really the least pressure I’ve ever had in a Tour stage,” Cavendish said. “Normally in the past, I’ve had a full dedicated team. Normally I win by some bike lengths. Today I had to lunge at the line, so you see that it wasn’t too easy.”
He also sought to dispel speculation that he might be looking ahead to the London Olympics.
“It (the Tour) is the most beautiful race of the year for me,” he said. “Here, it’s the Tour de France … I can’t say the Olympics are more important.”
Cancellara kept the lead for a third straight day after winning the opening-day prologue Saturday. Wiggins remains second, 7 seconds back, and Evans is a further 10 seconds behind in eighth place.
The riders’ only climbing challenge of the day was a winding, low-grade ascent up the citadel of Namur.
Three breakaway riders, including Anthony Roux of France whose injured left wrist hung limply by his handlebars, led for most of the day. The pack swallowed up Roux, the last to hold out, with a little less than nine miles left.