Jose Mourinho's fullback issue surfaced once more and caused his side plenty of problems, including the shackling of los Merengues' deadliest weapon—Cristiano Ronaldo.
Let's take an analytic glance at the proceedings.
Outside the comfort zone
Ronaldo has made the "left forward" position his home for both Real Madrid and the Portuguese national side.
He has his own unique spin on it, like Neymar does with Brazil and Santos, but the injuries to Marcelo and Fabio Coentrao have affected his game far more heavily than expected
We're very accustomed to seeing Ronaldo start wide on the left and drift inward, either looking for or whilst on the ball.
This "degree of freedom" is essential and helps the Portuguese forward get into the game and provide a threat, rather than being stuck out on the touchline.
His drifting is never an issue if Marcelo or Coentrao are manning the left-fullback position—their marauding forward runs give los Merengues efficient balance and width.
Unfortunately, Michael Essien cannot provide this balance.
He is far less willing to run forward and commit the opposing fullback—an understandable hesitation considering his natural position lies in central midfield—but it does leave Ronaldo limited.
Without the help of his fullback to detract attention and pull a marker, Ronaldo constantly found himself either one vs. two or even one vs. three.
Lukasz Piszczek and Sebastien Kehl took care of the £80 million man time and time again by outnumbering him and forcing him wide.
Ronaldo's solitary (and customary) goal was a simple ball over the top, but Madrid failed to get him into favourable positions during open play and during their long spells of possession.
The same cannot be said for Dortmund though.
Piszczek, as we know, is more than happy to overlap his right-winger, and this allowed Marco Reus to come inside with regularity. He saw more of the ball, took up good positions and allowed his Polish teammate to wreak havoc from the byline.
In the first 15 minutes of the second half, Piszczek crossed twice to give Mario Gotze and Sven Bender great chances from 18 yards out.Reus was able to drift inward and provide a viable passing option during these phases of play.
Reus and Ronaldo both played as a wide forward in a 4-2-3-1 formation, but they had very different games.
Here's some key stats from the game.
These figures are close, but it's evident that the German just shades it in terms of how heavily involved these two were.
The important comparison, however, must be made with the averages Ronaldo has accumulated so far.
In La Liga—a competition where Ronaldo has scored nine goals already—he averages 6.8 shots per game.
Tonight, he managed less than half the threat he usually poses defences.
He was cornered and nullified for large periods of the game, and while you can't blame Essien (he's a stand-in), the dearth of full-backs is a problem for Jose Mourinho.