Flavio de Luna from a Mexican selective team was the first atop the climb, which earned him the red jersey for the mountains classification leader at the end of the stage.

Upon the descent, the sprinters' teams Omega Pharma–Quick-Step, Cannondale, Androni Giocattoli–Venezuela and Lampre–Merida took station at the front of the peloton, bringing the escapees' advantage down to four minutes with 55 km (34 mi) remaining.

Mark Cavendish avoided the incident, launching from the Lampre–Merida train and won clearly, ahead of rivals Sacha Modolo and Alessandro Petacchi, to take a début victory for his new team, Omega Pharma–Quick-Step.

Sacha Modolo of Bardiani Valvole–CSF Inox derailed the big teams' plans as he beat rivals Mark Cavendish and Leigh Howard in the sprint.

[12] At the foot of the 8 kilometres (5.0 mi) long Mirador del Potrero ascent, Alex Correia Diniz of Funvic Brasilinvest–São José dos Campos attacked and maintained a slight advantage on the chasers throughout the climb itself, as the gradient increased.

The chase was led by a small group which dropped pre-race favourites Alberto Contador (Saxo–Tinkoff), Vincenzo Nibali (Astana) and Joaquim Rodríguez (Team Katusha) among others.

The overall classification leader changed once again as Michał Kwiatkowski (Omega Pharma–Quick-Step) recorded the third-fastest time for the course and claimed the race's lead from Alex Correia Diniz of Funvic Brasilinvest–São José dos Campos.

[17] Emmanuel Guevara of San Luis Somos Todos and Vojtěch Hačecký of ASC Dukla Praha broke away early and were given some freedom by the peloton since neither rider was a threat for the overall classification.

The stage was a double success for their San Luis Somos Todos team, since Díaz had gained enough time to move in the first spot of the general classification.

The course was then undulating until the uphill finish, commencing with a third-category climb immediately followed by the first-category Mirador del Sol, a 7 km (4.3 mi) long ascent at an average gradient of 8.75%.

[22] A breakaway of four riders formed, consisting of Marc de Maar (UnitedHealthcare), Mauro Finetto (Vini Fantini–Selle Italia), Adriano Malori (Lampre–Merida) and Pieter Weening (Orica–GreenEDGE).

[25] Going into the stage, the mountains classification was led by Emmanuel Guevara, but he had the same number of points (16) as Alex Correia Diniz, meaning the only categorised climb would determine the winner of that competition.

His team, San Luis Somos Todos, enjoyed other successes; adding to Guevara's mountains victory, Leandro Messineo won the sprints classification.