For 56 minutes, Manchester United had Real Madrid right where they wanted them. Cristiano Ronaldo and Xabi Alonso had been largely shackled; Michael Carrick was calmly conducting things from the base of United's midfield; Nani, Ryan Giggs and Danny Welbeck were everywhere.
An accomplished first-half defensive performance from Sir Alex Ferguson's team was rewarded when Sergio Ramos put one into his own net early in the second—the result of a slip from Raphael Varane that allowed Nani to send over a teasing cross.
Ramos' deflated expression as Old Trafford erupted spoke volumes. Jose Mourinho's Madrid were on the ropes and you sensed United were preparing to land a volley of follow-up punches. Confidence flowed as the crowd bayed for blood.
Madrid were, it seemed, going out.
Everything was going to plan for United until, with a flippant slide of his hand to his back pocket, the referee played a bigger role than any player before or after him in affecting the game's outcome.
Nani was trying to meet a high ball on United's right. He very well could have been aware of the incoming Alvaro Arbeloa in his peripheral, but his striking the Madrid player in midair with a boot was, at most, a yellow card.
Referee Cuneyt Cakir went red. It was a shocking decision that would come to define the contest, and it will be debated for years to come. Put simply, he got it spectacularly wrong and United paid the ultimate price.
With Nani went United's defensive shape and their chances of advancing to the quarterfinals.
With Ferguson fuming, Mourinho went almost immediately to his bench. On came the mercurial Luka Modric and, about 10 minutes after Nani's sending off, the sometime Croatian magician sent a wonderful curling shot beyond the clutches of David De Gea to bring the tie level at 1-1.
Mourinho deserves credit for bringing him on, as Modric opened the space necessary to deliver the most exquisite of finishes. But you couldn't help but feel United's coverage was compromised by the loss of Nani. Without him, they were stretched, and their Spanish visitors finally had space to breathe.
Soon after, Madrid killed the tie stone-dead. Gonzalo Higuain found space on the right and his driven cross was tapped in at the far post by Ronaldo—a clear beneficiary of Nani's departure for the free run he was allowed down United's left.
Ronaldo put his hands to his chest, respecting the fans who once came to worship him. The red card wasn't his fault, nor was it Madrid's. Old Trafford had only the referee to blame for a night that was undone by a baffling error of judgment.
Not even United could recover down 2-1, needing two goals from their 10 men with 20 minutes or so to play. They tried their damndest, but not even the introduction of Wayne Rooney could spark the kind of recovery Ferguson teams are famous for.
The battle was lost.
Madrid advanced and Mourinho's hopes of bringing them a 10th European title live on. United were left to count the cost of a lapse in officiating that undermined an entire season's effort.
It should have been a night to remember for the fabulous football played between two of the most storied teams in Europe, but a man named Cakir stole the headlines for all the wrong reasons.