In 2015 Nibali made the defense of his 2014 Tour de France title his priority.
His first notable result was 16th in the overall classification of Tirreno–Adriatico.
He then participated to the Amstel Gold Race and escaped thanks to a late attack, but was reabsorbed by the peloton and finished 65th.
In the La Flèche Wallonne, he tried an attack on the penultimate climb, but it failed and he finished 20th, only 19 seconds off the pace.
His first significant result of the year was placing tenth in the Tour de Romandie.

In June, he took part to the Critérium du Dauphiné, in which got a second place in the 6th stage and wore the yellow-blue jersey, which was lost the following day; after that, Nibali became the Italian National Champion for the second year in a row.
He attacked during the last ascent and got the better of Francesco Reda and Diego Ulissi.

He entered the Tour de France, but lost two and a half minutes to Chris Froome in the first week.
He lost a further 4:25 on the first mountain stage to La Pierre-Saint-Martin after he was dropped early in the stage; and was ninth overall after the three Pyrenean stages, trailing Froome by almost eight minutes.
As his hopes of a title defense had faded, he attacked in the Alpine stages and won the 19th stage from Saint-Jean-de-Maurienne to La Toussuire-Les Sybelles, after a 62-kilometre solo.
At the end of the stage Nibali was accused by Froome of unsportsmanlike behavior for attacking whilst Froome's bicycle had a brief mechanical problem 58 km from the finish.
It is not known whether Nibali was aware of the problem, since there was no communication from Radio Tour about the incident (as later stated by Astana manager Alexandre Vinokourov).
Television replays showed "Nibali twice glancing over his shoulder before accelerating away."
He finished the Tour de France in 4th place overall in the general classification, 8 minutes and 36 seconds down on the winner, Chris Froome.

Nibali also started the Vuelta a España, where he shared leadership of Astana with Fabio Aru, the eventual winner of the Vuelta.
On the second stage, however, Nibali was caught up in a large crash and was forced to chase hard to return to the peloton.
During the chase he held on to the team car, driven by the team's directeur sportif, Alexander Shefer, and was pulled up towards the main group.
Both Nibali and Shefer were disqualified from the race following the stage, with the team also fined.
The race director stated that he lamented the rider's "regrettable attitude".

In the autumn he won the Trittico Lombardo, taking solo victories in the Coppa Bernocchi and Tre Valli Varesine and placing second in the Coppa Ugo Agostoni.
In October he won his first Monument, the Il Lombardia, attacking on the descent of the Civiglio, the penultimate climb, and arriving solo ahead of Daniel Moreno and Thibaut Pinot.
In 2015 Nibali made the defense of his 2014 Tour de France title his priority. His first notable result was 16th in the overall classification of Tirreno–Adriatico. He then participated to the Amstel Gold Race and escaped thanks to a late attack, but was reabsorbed by the peloton and finished 65th. In the La Flèche Wallonne, he tried an attack on the penultimate climb, but it failed and he finished 20th, only 19 seconds off the pace. His first significant result of the year was placing tenth in the Tour de Romandie.
In June, he took part to the Critérium du Dauphiné, in which got a second place in the 6th stage and wore the yellow-blue jersey, which was lost the following day; after that, Nibali became the Italian National Champion for the second year in a row. He attacked during the last ascent and got the better of Francesco Reda and Diego Ulissi.
He entered the Tour de France, but lost two and a half minutes to Chris Froome in the first week. He lost a further 4:25 on the first mountain stage to La Pierre-Saint-Martin after he was dropped early in the stage; and was ninth overall after the three Pyrenean stages, trailing Froome by almost eight minutes. As his hopes of a title defense had faded, he attacked in the Alpine stages and won the 19th stage from Saint-Jean-de-Maurienne to La Toussuire-Les Sybelles, after a 62-kilometre solo. At the end of the stage Nibali was accused by Froome of unsportsmanlike behavior for attacking whilst Froome's bicycle had a brief mechanical problem 58 km from the finish. It is not known whether Nibali was aware of the problem, since there was no communication from Radio Tour about the incident (as later stated by Astana manager Alexandre Vinokourov). Television replays showed "Nibali twice glancing over his shoulder before accelerating away." He finished the Tour de France in 4th place overall in the general classification, 8 minutes and 36 seconds down on the winner, Chris Froome.
Nibali also started the Vuelta a España, where he shared leadership of Astana with Fabio Aru, the eventual winner of the Vuelta. On the second stage, however, Nibali was caught up in a large crash and was forced to chase hard to return to the peloton. During the chase he held on to the team car, driven by the team's directeur sportif, Alexander Shefer, and was pulled up towards the main group. Both Nibali and Shefer were disqualified from the race following the stage, with the team also fined. The race director stated that he lamented the rider's "regrettable attitude".
In the autumn he won the Trittico Lombardo, taking solo victories in the Coppa Bernocchi and Tre Valli Varesine and placing second in the Coppa Ugo Agostoni. In October he won his first Monument, the Il Lombardia, attacking on the descent of the Civiglio, the penultimate climb, and arriving solo ahead of Daniel Moreno and Thibaut Pinot.
Vincenzo Nibali