Last weekend's 3-1 Clasico defeat at home to Barcelona came as a psychological jolt to the world's richest club by revenue, who thought they had finally reached a point where they could land a blow on their arch-rivals.
Mourinho was brought in by Perez, a president not known for his patience with coaches, to end Barca's dominance of Spanish football a year and a half ago, but the Portuguese has only managed one victory over Barca in eight attempts.
Speaking at a Christmas lunch with the media on Wednesday, however, Perez was unequivocal in his support for the former Inter Milan and Chelsea boss.
"Signing Mourinho is one of the best decisions I have made," the construction magnate said.
"Aside from all his qualities, he has proven that he never gives up however great the challenge facing him. The Clasico defeat hurts, but it will make us stronger."
Madrid are level on 37 points with Barca at the top of the standings, in second on goal difference, but play their game in hand at the Sanchez Pizjuan on Saturday, while the champions compete at the Club World Cup in Japan.
Sevilla lie 13 points behind them in fifth place and boast one of La Liga's tightest defences. They held Barca to a 0-0 draw at the Nou Camp in October but are inconsistent and short on firepower.
VULTURES CIRCLING
While Mourinho received the full support of his president, the vultures are circling over a number of other coaches.
Villarreal's Juan Carlos Garrido, Atletico Madrid's Gregorio Manzano and Real Zaragoza's Javier Aguirre are all in need of morale-boosting wins.
Villarreal, who visit Osasuna on Sunday, came bottom of their Champions League group to exit Europe early last week. The pressure grew on Garrido when they could only draw against third-tier opposition in the King's Cup on Tuesday and are only kept out of the relegation places by goal difference.
Former Mexico boss Aguirre takes bottom club Zaragoza to Athletic Bilbao on Saturday having suffered seven defeats in the last eight league games.
Atletico's erratic form under Manzano and a 4-2 defeat away at Espanyol last weekend have led to speculation over his future. The lukewarm backing given to him sports director Jose Luis Caminero during the week only fanned the flames.
Media reports of a personality clash between Manzano and one of the team's most talented players, Jose Antonio Reyes, have not helped a side lying tenth, 10 points adrift of their end-of-season objective, the top four.
"I want to complete this project... if they let me," Manzano fired out in a tense news conference on Wednesday.
Atletico host Real Betis on Sunday.
