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.
Third seed Rafael Nadal remained on course for a 10th Barcelona Open title after reaching the quarter-finals with a 6-3 6-4 victory over Kevin Anderson on Thursday.
Barcelona were pitted against Italian champions Juventus in the Champions League quarter-final draw made on Friday to set up a repeat of the 2015 final which the Spanish side won 3-1.
Coach Luis Enrique blamed Barcelona's shock 2-1 La Liga defeat at lowly Deportivo La Coruna on the exertions of their sensational midweek 6-1 Champions League win over Paris St Germain.
Barcelona suffered a hangover from their remarkable Champions League comeback against Paris Saint-Germain as Alex Bergantinos's winner 16 minutes from time handed Deportivo la Coruna a famous 2-1 win on Sunday.
Few believed Barcelona could achieve the impossible against Paris Saint-Germain, including former German international and ex-Barcelona star Bernd Schuster.
Barcelona's amazing 6-1 victory over Paris St Germain on Wednesday that sent them through to the Champions League quarter-finals will forever stay in the memories of supporters, coach Luis Enrique said.
Lionel Messi and Sergio Aguero will lead Argentina's bid to resurrect their flagging World Cup campaign in crucial qualifiers against Chile and Bolivia later this month.
Barcelona must believe in their ability to make history as the first Champions League team to overturn a 4-0 first-leg deficit when they line up against Paris St Germain at Camp Nou on March 8, captain Andres Iniesta said on Monday.
Lionel Messi could not be happier than at Barcelona, and can crown his status as an all time great by winning the World Cup with Argentina, national coach Edgardo Bauza told AFP on Wednesday.
Neymar, Barcelona and Santos will stand trial on fraud and corruption charges over the transfer of the Brazilian forward after their appeals were turned down by Spain's High Court on Monday.