Los Blancos can advance to Wembley Stadium on May 25 with a 3-0 win. If Dortmund scores at all, Real will have to win by at least four goals to advance. A 4-1 win for Real would go to extra time, but any other result would send Dortmund to the finals.
So the odds may be stacked against Ronaldo and company, but they're certainly not going to go down without a fight.
Here are the keys to Los Blancos pulling off the incredible upset:
Set the tone early
A goal in the first 15 minutes for Real would be an ideal way to start the game. With such an uphill climb, Los Blancos must get started early.
In the first leg of the semifinal, Los Blancos didn't get on the board until the 43-minute mark, when Ronaldo scored the only goal of the game for Real.
That goal tied the game at 1-1, but Robert Lewandowski of Dortmund scored three of his four goals in the second half to put the game away.
If Los Blancos get a goal on the board first this time, they can set the tone for the entire match.
Shut down Lewandowski
With four goals in the last match, Lewandowski had his way with Los Blancos in the first leg.
Dortmund will likely look to him again to take them to the finals, so Real must make the necessary adjustments.
The best way to take Lewandowski out of the game is to simply keep the ball away from Dortmund all together. Even though they have to win by at least three goals, possibly four, Los Blancos must be methodical about their approach on offense.
If they can maintain control of the ball, the goals will come.
Utilize home-field advantage
It sounds cliche, but Real must take advantage of being on its own turf in a game where they'll have to battle the whole game.
Scoring three goals while holding the team scoreless is hard enough. If Los Blancos allow even a single goal, they'll need to win by four.
That means for all 90 minutes, Real must play at a fast yet controlled paced.
At the end of the day, the most important thing is that Los Blancos can't get down on themselves. If things don't go their way early in the game, they can channel the crowd to re-energize themselves.