A 2-1 win in Germany and a 2-2 draw in Spain would be enough to see Borussia Dortmund into the Champions League final at Wembley next month.
Those were the results when they met Real Madrid prior to Christmas in the group stages of the same competition.
Things have changed a bit since then though. Los Blancos have rediscovered the form which saw them win La Liga last season, losing only twice since the turn of the year and with an eye fixed intensely on their 10th European Cup—La Decima.
Cristiano Ronaldo has redoubled his efforts since saying "Feliz Ano a todos" (Happy new year) and he and his teammates have moved on from the early-season struggles which effectively ended their hopes of defending the La Liga title.
At the Westfalenstadion on Wednesday night, the Portuguese forward will play his 24th game of the calendar year for his club side. Prior to the turn of the year—not including the SuperCopa—he played had 24 games in the 2012/13 campaign.
In the first set of 24 matches he scored 21 goals. Before completing his second set of 24 in Dortmund this week, he's already managed a further 27 and heads into the first leg as the competition's top scorer with 11 goals in 10 appearances.
Previous matches against Dortmund this season though haven't been as fruitful as on most occasions when Ronaldo has adorned the Madrid shirt.
WhoScored have his match rating for both games as below seven. It's always better to watch and make your own mind up than take other's ratings, but it is telling given the frequency in which the 28-year-old records scores of eight or more.
He scored the equalizer in the 2-1 defeat in Germany but failed to register in the 2-2 draw at the Bernanbeu—of six shots only one was on target.
His direct rival in those games was the Polish right-back Lukasz Piszczek, a player with two goals and nine assists this season. Although a look at his action zones vs. Cristiano Ronaldo in the match at Dortmund show how disciplined defensively the Polish international had to be to marshal Madrid's No. 7:
Compare this with how much the 27-year-old got forward against Mainz at the weekend. Admittedly it's a completely different scenario, but the point still stands:
Regardless of the previous two meetings this season and Piszczek's solid defensive performances, Cristiano Ronaldo will still be able to hurt Borussia Dortmund over 90 minutes.
There is only so much Piszczek—or any of the world's best full backs—can do to contain him. Ronaldo's game has exploded since Christmas and the big stage, where he was once doubted (via Eircom Sports), has become his.
Barcelona, Manchester United and Galatasaray have all been the receivers of fatal blows in the last two months.
If Ronaldo is being suffocated on the left, then he can divert his runs through the middle, he can switch to the right or he can simply redouble his efforts.
But it's not just from open play where he can hurt Dortmund. He can strike set pieces from up to 40 yards out and he's dangerous in the air from corners and free kicks.
The Germans did exceptionally well to contain him and Madrid when they last met, but there's now a ruthlessness and an ambition which previously eluded the Spanish champions towards the end of 2012.
With that mentality back, expect Cristiano Ronaldo to inflict the hurt on Jurgen Klopp's men which was missing in the group stages.