The 24-year-old Italian won two mountain stages of this year's Tour de France and was sitting ninth in the overall standings.
But Saunier Duval withdrew all their riders from the stage and have now pulled out of the race.
As a consequence of Ricco's withdrawal, Italian Vincenzo Nibali of Liquigas took the white jersey for the best young rider and German Sebastian Lang of Gerolsteiner the polka dot jersey for best climber.
French riders Samuel Dumoulin and Arnaud Gerard broke away from the peloton after 25km of Thursday's relatively flat stage and stayed away until the final 10km.
On a flat transitional stage between the Pyrenees and the Alps, the bunch was happy to let them remain out in front, though the duo were joined by Spain's Juan Jose Oroz with 50km remaining.
Yellow jersey holder Evans was content to stay in the peloton and monitor Frank Schleck, whom the Australian leads by just one second.
The peloton, making the most of a strong tailwind, caught the leading trio in the closing stages before Cavendish surged to victory.
Stage 12 results, Lavelanet to Narbonne (168 km):
1. Mark Cavendish (GB/Columbia) 3h 40m 52s 2. Sebastien Chavanel (Fra/Francaise des Jeux) same time 3. Gert Steegmans (Bel/Quick-Step) same time 4. Erik Zabel (Ger/Milram ) same time 5. Oscar Freire (Spa/Rabobank ) same time 6. Francesco Chicchi (Ita/Liquigas ) same time 7. Thor Hushovd (Nor/Credit Agricole ) same time 8. Leonardo Duque (Col/Cofidis ) same time 9. Julian Dean (NZ/Garmin - Chipotle) same time 10. Heinrich Haussler (Ger/Gerolsteiner) same time
Selected others: 49. David Millar (GB/Team Garmin-Chipotle) same time
Overall standings (after 12 stages):
1. Cadel Evans (Aus/Silence - Lotto) 50 hours, 23 minutes, 5 seconds 2. Frank Schleck (Lux/Team CSC) :01. 3. Christian Vandevelde (US/Garmin - Chipotle) :38. 4. Bernhard Kohl (Aus/Gerolsteiner) :46. 5. Denis Menchov (Rus/Rabobank) :57. 6. Carlos Sastre (Spa/Team CSC) :1:28. 7. Kim Kirchen (Lux/Col) :1:56. 8. Vladimir Efimkin (Rus/AG2R) :2:32. 9. Mikel Astarloza (Spa/Euskaltel) :3:51. 10. Vincenzo Nibali (Ita/Liquigas) :4:18.
Selected others: 47. David Millar (GB/Team Garmin-Chipotle) :24:32 147. Mark Cavendish (GB/Team Columbia) 2:27:26
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