Barcelona and Osasuna appealed against the decision to play the game on Thursday after it was initially postponed on March 8 following the death of a doctor at the Catalan club, but their pleas were ignored.
Barcelona were 4-2 down towards the end of the match before goals from Robert Lewandowski, Eric Garcia and Raphinha secured their comeback.
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
Arsenal forward Alexis Sanchez is keen to play the same kind of role Lionel Messi performs at Barcelona, the Chilean international said.
Spanish giants FC Barcelona sealed a massive shirt sponsorship deal Wednesday with Japanese online retailer Rakuten worth at least 55 million euros ($59 million) a year.
Barcelona president Josep Maria Bartomeu predicts that Lionel Messi would not only extend his contract with the Catalan club but also end his playing days there too.
Lionel Messi announced a press boycott to protest against a journalist who alleged team-mate Ezequiel Lavezzi had used marijuana at Argentina's training base.
European Golden Shoe winner Luis Suarez said negotiations to extend his contract with Barcelona until 2021 were running smoothly.
Stars of Emmy-winning television epic "Game of Thrones" got a front row seat at the Lionel Messi show on Sunday as the Argentine superstar scored his 500th Barcelona goal.
After beating the 'best team in the world', playing lowly Middlesbrough on a November afternoon in the north of England should bring Premier League leaders Manchester City nicely back to earth.
Barcelona will put Manchester City to the sword if they commit the same kind of errors as they did in their Champions League encounter last month, coach Luis Enrique has said.
Barcelona centre-back Jeremy Mathieu joined the club's mounting injury list and faces three weeks out after hurting his right calf,
Barcelona's Uruguayan star Luis Suarez on Thursday collected the Golden Shoe award for the leading scorer in Europe last season
