For many, it was a single moment of pain amid an evening of utter elation. The only blemish on a performance ranking among the most devastating in years.
Already 3-0 ahead with a paltry 38 minutes on the clock inside the Allianz Arena, Xabi Alonso's yellow card—one that would rule him out of the Champions League final—for a challenge on Bayern Munich's Bastian Schweinsteiger left everyone connected with Real Madrid to expel a deep groan.
Lost for the club's most pivotal evening in more than a decade, the midfield enforcer's importance to Los Blancos was neatly encapsulated by the widespread dismay of his impending absence.
When crosstown rivals Atletico Madrid were announced as the club's opponents for the decider, "How will Real combat Atleti's robust system without Alonso?" quickly became the burning question.
In truth, Carlo Ancelotti's side barely found a way at all; an underdone Sami Khedira watching the game largely pass him by as he filled Alonso's role.
It's often true that one's absence highlights their precise value more than their presence can.
"Don't it always seem to go, that you don't know what you've got ‘til it's gone," Joni Mitchell sung, after all, in her 1970 hit "Big Yellow Taxi."
Had you silenced the crowd inside the Estadio da Luz in Lisbon on May 24, you might have even heard Mitchell's iconic lyrics playing softly until Sergio Ramos' last-gasp intervention.
It's important to remember such evenings—particularly those that are recent—when doubts suddenly descend over a player as esteemed as Alonso.
On Tuesday, it was reported by El Confidencial, as relayed by the Daily Mail, that Ancelotti and Real Madrid were harbouring concerns over the fitness of the Basque midfielder, leading to speculation that the European champions could look to sell the 32-year-old.
The contradictory, hyperbolic galaxy that is the summer transfer window, of course, should always be kept at a respectful distance. Just two weeks ago, football fans were being told Lionel Messi had sounded out Arsenal, per Graeme Yorke of the Daily Mail.
But if there is validity to the reports surrounding Alonso, the alarm bells might be warming up at the Bernabeu.
Last season, Alonso's return from injury coincided with a distinct up-turn in form for Los Blancos. After missing his strong tackling, searching distribution and his calm sense of control, Ancelotti's midfield clicked when the veteran established himself beside Luka Modric from November onward.
And it's those qualities that were missed which distinguish Alonso from the plethora of midfielders in Real Madrid's stable.
In Modric and new signing Toni Kroos, Ancelotti has two gifted playmakers more comfortable when pushing forward. In James Rodriguez, the club's latest Galactico, Real have a precocious out-and-out No. 10. Ditto for Isco.
Angel di Maria, meanwhile, is an explosive converted midfielder who was once a winger, while Khedira's future looks as certain as Iker Casillas' starting place.
Among the holding options, Asier Illarramendi is yet to show he's the elite midfielder Real had believed he was, while Casemiro has been sent to Porto.
While that cast—an ensemble so heavily skewed in favour of attack—will overrun the minnows of La Liga, major European rivals will pounce on the obvious, soft underbelly.
If Real Madrid are to achieve any sort of balance in 2014-15, Alonso's ongoing existence in the Spanish capital is paramount.
Concerns over Alonso's fitness have perhaps been exacerbated by more recent on-field evidence, particularly the veteran's underwhelming performances with Spain at football's showpiece in Brazil.
Swamped in midfield by a tactically superb Netherlands, and then again by a ferocious Chile, the 32-year-old appeared decidedly sluggish in comparison with La Roja's opponents.
But the Spanish team is not Real Madrid. Don't confuse La Roja with Los Blancos.
Against the Dutch, Vicente del Bosque deployed Alonso on the same field as Xavi, Andres Iniesta, Sergio Busquets and David Silva. Fine technicians they may be, but more raw athleticism can be found at your local bowls club.
Alonso, therefore, wasn't complemented by contrasting teammates; his ability to control proceedings as the deepest member of an otherwise explosive attack was negated.
As he prepares to step out onto the turf at the Bernabeu—assuming he stays in the club's possession—the situation will be vastly different to those nights in Salvador and Rio de Janeiro. Ahead of Alonso will be Europe's most lethal front three, comprised of Cristiano Ronaldo, Gareth Bale and Karim Benzema. Joining him more centrally at various stages will be the youthful legs of Rodriguez, Kroos, Isco and possibly Di Maria.
In short, Alonso will be surrounded by an array of physically sound athletes and be allowed to do what he does best: Tackle hard, utilise his supreme passing range and cover the gaps.
In his absence, however, Los Blancos will lose the sense of control he provides, the variety his game brings and balance he gives to Ancelotti's formation
In his absence, Real Madrid could even lose their grip on Europe, too.