Madrid have been embarrassingly knocked out at the same last-32 stage for the last two seasons, both by other Segunda Division B sides in Real Union and Alcorcon, and having been held 0-0 in the first leg by Murcia, another shock is not out of the question.
Mourinho will be desperate to avoid that and hopes the Bernabeu can play its part.
"I know it's difficult but I would like a hotter Bernabeu," he said. "I'm not asking for an atmosphere like the one at the San Siro in the Milan-Real Madrid game, I know that it's a question of culture, but I would like to see the Bernabeu a little hotter.
"The players deserve a little more support and Wednesday night could be a good opportunity for that. With an almost full stadium and with a good pitch, not like in the first leg, we ought to win.
"The game has pressure, responsibility and danger. The match against Murcia is the most important of the season so far because it's the only one in which we could get knocked out of a competition.
"If you lose a Champions League game you have five more. And if you do it in La Liga, you have 37 more. After the bad result of the first game this encounter is more decisive. If we lose we are out, the same as if we have a score draw.
"Our only possibility is to beat them and we are obliged to get through.
"I'm not thinking about being eliminated. I think that two goals will be sufficient, but one would be very risky. They have a spectacular defence."