PARIS, September 13- Barcelona and AC Milan, with 10 European Cup and Champions League titles between them, suffered embarrassing defeats at the weekend as Europe's formbook was turned upside down.Spanish champions Barcelona slumped to a shock 2-0 home defeat at the hands of Hercules, who are in the top flight for the first time in 13 years, while, in Italy, Cesena, also a promoted team, stunned Milan 2-0.
Paraguayan forward Nelson Haedo Valdez, signed from Borussia Dortmund, grabbed both Hercules goals to hand Barcelona their first home defeat since May 23, 2009.
Barcelona coach Pep Guardiola refused to make excuses for the Hercules setback with the match coming after a two-week interval for Euro 2012 qualifiers.
"There have always been international breaks and we didn’t fail to win because of that," said Guardiola.
"I see how the players work every day and I don’t have any doubts about this team."
Defeat was also a bitter disappointment for Argentina’s Javier Mascherano who was making his Barcelona debut following his 22-million-euro move from Liverpool.
Jose Mourinho celebrated his home debut as Real Madrid coach with a 1-0 win over Osasuna thanks to a goal from Portuguese compatriot Ricardo Carvalho.
However, the demanding Santiago Bernabeu crowd jeered Real for their dogged performance.
"The public can jeer if they want and I can respect it," said Mourinho.
"I work for the total satisfaction of the public and they pay me to work and not to criticise the fans. I will never say anything against the fans of Real Madrid."
Atletico Madrid and Valencia lead the way in Spain with six points from two matches after wins over Athletic Bilbao and and Racing Santander respectively.
Cesena, who were in the Italian third division just two seasons ago, moved into the top four in Serie A after their 2-0 win over AC Milan with goals from Erjon Bogdani and Emanuele Giaccherini.
Big-money signings Robinho and Zlatan Ibrahimovic, who missed a penalty, suffered nightmare debuts for Milan.
"The team needs to have a completely different attitude. We need sacrifice, especially when you go behind," said Milan coach Massimiliano Allegri.
Champions Inter Milan secured their first league victory with a 2-1 success at home to Udinese with Samuel Eto’o scoring the winner after Antonio Floro Flores had cancelled out Lucio’s early opener.
"Of course the important thing was to win," said Inter coach Rafael Benitez. "We had a very good start but then we lost control in midfield and they had some dangerous counters."
Chievo are the unlikely early pace-setters as they won 3-1 away to Genoa despite going a goal down.
German champions Bayern Munich are also struggling and are already five points behind leaders Hoffenheim after a dull goalless draw with fellow Champions League representatives Werder Bremen.
Mainz are second behind Hoffenheim on goal difference after a 2-1 win over Kaiserslautern kept up their perfect start.
In France, Toulouse lost their 100-percent record in a 1-0 home defeat to Saint-Etienne but still lead the way by a point.
Uruguayan striker Luis Suarez converted two penalties to give Ajax a 2-0 win over bottom side Willem II to keep the Amsterdam giants on top of the Dutch first division.
PSV are just behind on goal difference after a 3-1 come-from-behind win over NEC Nijmegen.
FC Porto beat Sporting Braga 3-2 to stay top in Portugal with four wins from four.