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
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.
Barcelona boss Luis Enrique labelled harsh treatment dished out to his players by Barca fans nonsensical as the Spanish champions squeezed past Leganes 2-1 on Sunday.
Real Madrid coach Zinedine Zidane warned that it was still all to play for in their Champions League last-16 clash against Napoli after the holders strolled to a 3-1 win in the first leg on Wednesday.
Atletico Madrid will have to win at Barcelona's Nou Camp for the first time in a decade on Tuesday if they are to reach the King's Cup final.
Barcelona midfielder Rafinha faces a spell on the sidelines after suffering a broken nose in a clash with his own goalkeeper Marc-Andre ter Stegen in Saturday's 3-0 win over Athletic Bilbao.
Lionel Messi struck another trademark free-kick as Barcelona moved to within a one point of La Liga leaders Real Madrid with a 3-0 win over Athletic Bilbao on Saturday.
Luis Suarez and Lionel Messi scored stunning goals to edge Barcelona towards a fourth consecutive King's Cup final with a 2-1 win at Atletico Madrid on Wednesday, although the holders were lucky to survive a late onslaught from the hosts.
Diego Maradona has revealed his drug problems began when he was at Barcelona in the 1980s in an interview with an Italian private television network, Canale 5.
Barcelona ended a decade-long drought without winning away to Real Sociedad on Thursday as Neymar's first-half penalty handed the Spanish champions a 1-0 Copa del Rey quarter-final, first leg lead.
