Danny Welbeck's away goal could be crucial heading into the return leg at Old Trafford, and it must be said Sir Alex Ferguson played an incredibly tactically reactive game on Wednesday.
Let's score the key tactical battles on the field.
This was the battle we'd all been waiting for.
Manchester United opted for a 4-2-3-1 formation, then switched to a 4-4-2 in the second half. Phil Jones did not occupy any kind of midfield diamond slot, and instead played on the right side of a pivot with Michael Carrick.
Cristiano Ronaldo was left to battle Rafael one versus one on the outside—a battle he frequently won—but Jones closed down the space he could work in very well once he cut inside.
It's telling that the breakthrough goal, scored by the Portuguese, came when he temporarily swapped wings.
Winner: Phil Jones
Exactly what was Shinji Kagawa's role on Wednesday night?
It's tough to put your finger on it, but initially Manchester United lined up in a very loose, lopsided 4-2-3-1 with the Japanese playmaker playing behind the striker.
He tried to drift into the space between the holding pivot and the defensive line, but it wasn't often he achieved it, and when he did, he wasn't found.
The Red Devils have immense difficulty through the middle of the park for long periods of the game, and playing with Kagawa there was like playing with 10 men.
After halftime they switched him out to the wing in a flat 4-4-2, but he was not the foil his full-back needed.
Winner: Xabi Alonso and Sami Khedira
When Nemanja Vidic's name was nowhere to be seen in Manchester United's lineup, a small amount of panic descended over supporters.
The faith Sir Alex Ferguson places in Jonny Evans is astounding, and the Northern Irishman stepped up in a massive game and played an unbelievable 90 minutes.
He battled, he harassed, he challenged and he fought his way to the finish line, besting Karim Benzema and Gonzalo Higuain in confident fashion.
Los Blancos' were limited to second balls, pot shots and scraps. That's due to the Evans-shaped wall that stood in the way of the conventional route to goal.
Winner: Jonny Evans
Moving away from the individual battle of Phil Jones vs. Cristiano Ronaldo, there was a war raging on one particular flank involving four or five players at all times.
Manchester United's right (Rafael, Rooney and then Valencia) came up against one of the most experienced left-sided duos in world football in Ronaldo and Fabio Coentrao, and struggled for long periods.
Had Coentrao's shot that struck the inside of the post found the back of the net, it would have been a very different game. Rafael in particular had a very bad day at the office.
It was a surprise to see the Brazilian even come out for the second half, as against Reading he was substituted around the 30-minute mark after picking up a booking and was left teetering on the edge.
Madrid didn't test this flank enough in the closing stages, but virtually every breakthrough—bar Ronaldo's goal—came down this touchline.
United can thank Jonny Evans that it didn't lead to goals.
Winner: Real Madrid's left