The 62-year-old Mazzarri became the second man to be sent packing this season by the ailing Italian champions.
Girona defeated their Catalan rivals for the first time ever in the top flight in a pulsating battle to rise two points above Real Madrid, second, after their 1-1 draw at Real Betis on Saturday.
Champions Barca were dominating the match early on under the scorching heat of south Madrid, with Brazil winger Raphinha the main threat to the home side's defence by running the right channel and creating several opportunities.
Barca's friendly against Juventus, due to be played later on Saturday, was cancelled after an outbreak of viral gastroenteritis among the Spanish team
Xavi's side wrapped up the title after two first-half goals from Robert Lewandowski spurred them to a 4-2 win against city rivals Espanyol on Sunday
UEFA opened a formal investigation into Barcelona last month for potential violation of the European soccer governing body's legal framework regarding payments made by the club to a company owned by a senior refereeing official
Barcelona beat Real Madrid 1-0 in the Copa del Rey semi-final first leg on Thursday at the Santiago Bernabeu, but were criticised for only having 34 percent possession
Fernandes told BT Sport. "The belief of the fans, they push us through difficult moments. We have made great comebacks, the club is made also by that. In the past we have done a lot like this result"
Mexico's Pumas on Saturday signed Dani Alves after the veteran Brazilian defender left Barcelona for a second time.
Barcelona's forward line of Lionel Messi, Luis Suarez and Neymar is the best in the history of the club, according to David Villa.
Lionel Messi will miss Barcelona's Club World Cup semifinal with Guangzhou Evergrande due to renal colic, the club has announced.
Manchester United's executive vice-chairman Ed Woodward is "desperate to land Neymar," while "Woodward's rival at City, Khaldoon Al Mubarak, is working just as hard to pull off the biggest transfer coup in history for Messi."
Barcelona star Neymar said he doesn't fear passionate Real Madrid fans at the Estadio Santiago Bernabeu for the Saturday's El Clasico.
For this weekend, Neymar and Suarez must prove Barcelona can win El Clasico without the rivalry's all-time top scorer Lionel Messi.
Neymar could be forced to leave Barcelona due to his ongoing tax fraud case, according to the Brazilian's father.
Barcelona star Leo Messi races against speedster Usain Bolt and American Pharoah, the first horse to win the Grand Slam of American horse racing, for the Sports Illustrated's annual prize.
Barcelona defender Gerard Pique has hailed the selflessness of Lionel Messi, Luis Suarez and Neymar and believes the trio's lack of ego is key to their success.
Barcelona president Josep Maria Bartomeu says star forward Lionel Messi is on course to be fit to face Real Madrid on November 21.
Luis Suarez scored either side of a Neymar double as Barcelona cruised to a 3-0 Champions League victory over BATE at Camp Nou.