Los Blancos reached the 100-goal mark in the league this season as they shifted the pressure back on to Barca in the battle for La Liga with a comprehensive victory in Pamplona
Karim Benzema netted the first of the night with a stupendous volley before Cristiano Ronaldo and Gonzalo Higuain extended Madrid's lead before the break. Osasuna clawed a goal back early in the second half through Nino, but it was in vain as Ronaldo and then Higuain completed the rout, ending the Navarrans' six-game unbeaten streak.
Benzema fired Los Blancos ahead with a truly remarkable strike, connecting with Ronaldo's deep cross. The ball hung in the air, allowing the Frenchman to set himself up before showing perfect technique as he unleashed an unstoppable volley into the opposite corner from a tight angle.
In pursuit of a second, Madrid counterattacked at pace ending in Ronaldo's dipping effort narrowly missing the target. The visitors had manufactured the chance after the referee had let play continue following Esteban Granero's crunching tackle, a challenge that Mendilibar contested, resulting in the Osasuna coach being sent to the stands.
As the quality of play subsided, the Navarrans drew a number of fouls, one of which saw Sergio Ramos harshly cautioned, ruling the defender out of Valencia's visit to the Bernabeu next weekend.
Ronaldo then explosively put his side two up as he netted his first-ever goal at the Reyno de Navarra. Picking the ball up all of 40 yards from goal, the Portuguese international took one look before rifling a stunning effort into the top corner.
Mourinho's side found a third not long after when Xabi Alonso's precise pass found Higuain. The Argentine international, clean through, provided a cutely clipped finish over Andres Fernandez to net his 100th Madrid goal five minutes before the break.
Dejan Lekic was introduced for the second half as Osasuna looked to reduce the three-goal deficit, which they did after just two minutes. Roversio won the ball deep in Madrid territory before crossing toward the far post where Nino was on hand to send a bullet header past Casillas.
Higuain would have re-established Madrid's three-goal cushion after rounding Fernandez, but for a moment of pure comedic value. Ronaldo collided with the Argentine as both men looked to provide the finishing touch, but instead they watched in despair as the ball trickled behind for a goal kick.
Osasuna remained in the ascendancy as the half progressed but Madrid always threatened on the break, and Los Blancos were awarded a free kick on the edge of the area after a fluent counter. Ronaldo stepped up and drilled in a low strike that took a deflection to wrong-foot Fernandez as he registered his 37th Liga goal this season.
The Portuguese then turned provider with beautiful footwork on the wing, as Madrid put the game to bed. The former Manchester United man danced past his marker before presenting Higuain with the easiest of headers to double his goal tally for the evening.
As the game drew to a close Roland Lamah was shown two consecutive yellow cards as Osasuna finished the match with 10 men.
Madrid's five strikes on the night saw them reach the 100-goal mark in La Liga this season, now just seven shy of their club record. Mourinho's side return to Champions League action in midweek against APOEL, whilst Osasuna face Rayo Vallecano next weekend.