After an outstanding attacking display at the Westfalenstadion last Wednesday, Borussia Dortmund arrive in the Spanish capital with a 4-1 lead over Real Madrid and one foot practically in next month's final at Wembley.
However, despite their rather limp display in Germany, it would be foolish to completely write off Los Merengues, for whom the pursuit of the Decima has been all-consuming this season.
Victory in the Madrid derby against local rivals Atletico on Saturday evening at the Vicente Calderon will have been just the tonic required to give Madridista supporters hope that a remarkable rescue act can be performed on Tuesday.
With that in mind, here's a look at five things that the nine-time European champions must do if they're to rectify the wrongs of their German nightmare and to stand any chance of taking part in the Champions League final on May 25.
It was Dortmund who flew out of the traps last week, putting Real Madrid on the back foot from the word "go" with their high-tempo, high-pressure style and no shortage of attacking quality.
Now, the shoe must reside on the other foot. With Madrid needing three goals (minimum) it is a necessity that they stamp their authority on proceedings straight from the first whistle.
Jose Mourinho's side experienced firsthand the damage that a quick start can do, both in the first period as well as the second.
With the speed of Sergio Ramos and/or Pepe or Raphael Varane expected to start in the center of the back four, Madrid can afford to press with a high defensive line. As such, they'll be able to compress the game in the Dortmund half, putting pressure on an opposing defence that has been far from infallible across the course of the current campaign.
Should Real return the favour and start the game at a lightning-quick pace, then they'll not only get the home support firmly on their side, but may just be able to unsettle Jurgen Klopp's side.
When Luka Modric was signed from Tottenham Hotspur last summer, it was widely hailed as something of a coup.
Last season's Champions League semi-final loss to Bayern Munich has illustrated that Madrid needed a greater command of possession, someone who could dictate play from a position further forward whilst also dropping deep to work in tandem with Sami Khedira and Xabi Alonso. For all his qualities, Mesut Ozil is an outstanding No. 10, but can get lost when a match isn't running in his side's favour.
With that in mind, Modric appeared to be the perfect solution.
However, the 27-year-old has struggled to make an impact in Madrid—a 30-minute cameo in Manchester aside.
He once again proved more a hindrance than a help during the first leg in Dortmund, appearing decidedly unsure about his role, whilst his selection meant Ozil was shunted to the right-wing to accommodate the Croatian international.
Thus, with Madrid's need to press Dortmund, and Angel Di Maria having scored twice at the weekend, a recall for the Argentine winger and a return to his preferred role for Ozil, at the expense of Modric, would be the logical move.
In becoming the first player to ever net four times against Real Madrid in the history of the European Cup, Robert Lewandowski was undoubtedly the star of the show in the first leg.
Neither teenage prodigy Raphael Varane nor his more experienced partner Pepe were able to get to grips with the Polish striker, whose combination of stealthy movement and finishing prowess have put his side firmly in the ascendancy.
Pepe has not enjoyed his best season at the club, having been very much in and out of the starting 11, whilst Varane, who has enjoyed a meteoric rise, has suffered from a dip in form in the past six weeks or so.
Alvaro Arbeloa's return from suspension would have allowed Sergio Ramos to return to his preferred role in the centre of defence had it not been for the fact that the former Liverpool full-back will miss the game anyway through injury.
Thus, Ramos will remain at right-back, leaving Pepe and Varane in tandem to deal with Lewandowski once again. They'll need to impose themselves on the Dortmund No. 9 much more than they did in the first leg if they're to stop him causing havoc once again.
No question that the midfield battle in the first leg was won by the home side, with Ilkay Gundogan the dominant figure in that area.
On the contrary, it was a poor night for Madrid's playmaker-in-chief Xabi Alonso. Unable to find any space from which to dictate play, his passing was far from its usually impeccable standard, whilst he was also directly responsible for Dortmund's fourth goal, giving away a penalty with a needless challenge on Marco Reus.
Whether it was due to the overcrowded nature of the midfield zone—Luka Modric's appearance and tendency to drop deep meant there were often times when all six players designated in that area from the two sides were within 20 yards of one another—is debatable, but the usually cool Alonso was far from his normally unruffled self.
Unquestionably, Los Galacticos need to free up space from where Alonso can do his best work, whilst movement ahead of the former Liverpool and Real Sociedad man needs to be much greater than it was last week.
With Madrid almost certainly set to dominate possession at the Santiago Bernabeu, they'll need Alonso to be at his very best if they're to make that domination count.
With 12 goals in the Champions League so far this season, Cristiano Ronaldo is the tournament's top goalscorer and has been an integral part in Madrid's run to the semi-final stage.
Yet, whilst he got his name on the scoresheet in the first leg and tested Roman Weidenfeller with a couple of long-range efforts, he was unable to have any major impact on Dortmund's defence.
Unquestionably, that must change.
Criticism of the world's most expensive player has long revolved around a supposed tendency to go missing in big games.
Over the past 18 months, he has answered those critics with crucial goals and big performances aplenty.
He needs another top-quality display if he is to lead from the front and drag Jose Mourinho's side to what is currently a seemingly unlikely appearance at Wembley.