The Portuguese coach made the strange decision not to face the media after his side's excellent 3-1 win at Camp Nou on Tuesday night, sending his injured skipper instead
The Portuguese coach was widely expected to make an appearance after a Ronaldo double and a headed goal from Raphael Varane ensured qualification for the Copa del Rey final, regardless of Jordi Alba’s late consolation.
Casillas, who has been out of action with a hand injury since mid-January and is expected to return two weeks into March, hailed the Portugal international’s impact and hopes this win mends wounds caused by their poor Liga performances.
"We decided it's a good time to bring up the captain," the Spain international said to reporters after the game. "We realise that we will not win the title, but it’s a good time to converse publicly with the Blancos fans considering our level in the league.
"This gives us more peace for the rest of the season. Barcelona did not look as good as Madrid. The team were brilliant defensively. Cristiano Ronaldo has also been crucial."
Casillas went on to suggest he wants the former Manchester United winger to stay at the Bernabeu despite reports linking him with a move away, and the skipper wants the win to propel the club on to better things this season.
"Real Madrid have beaten Barcelona tactically," he added. "Cristiano Ronaldo is proving its importance in the Real Madrid. He’s our most important player. He’s already demonstrated his level in other Clasicos, too.
"[Will he renew his contract?] He will have to deal with that issue with the club, but for us it would be a joy.
"Cristiano Ronaldo is a vital player, and he is going through a very good run. But all the team have been very good. Such an approach needs to be taken to Old Trafford. It’s 1-1 and it’s also a stadium in which we like to play.
"Hopefully it's a turning point and we can enjoy it at Real Madrid. After beating Barcelona, we can hope to make a progress in the Champions League. This will help."
Mourinho's men will face Barcelona on Saturday for another Clasico, though this one will be of less importance to Madrid with a crucial Champions League fixture around the corner and the Liga title seemingly out of reach.
However, Casillas has called for concentration, adding: "When you see that the league is not going well, the players might not be 100 per cent [up for it], with the Copa del Rey and the Champions League also a challenge.
“But next up is another Clasico and we must win that to cut the points advantage [that Barcelona have].
"I know the Barcelona players, and I know they are competitive. Clearly two losses [after AC Milan’s win in the Champions League last week] are significant.
“Perhaps as a result of Liga form, fans and players of Barcelona did not expect [us to win tonight]."