In a helter-skelter game, the noises of disapproval focused on the captain, rather than Cristiano Ronaldo, whose penalty was saved by the excellent Alves, or Gareth Bale, who struck the crossbar.
It will be scant consolation to Casillas, but he is unlikely to have to endure boos louder than the applause he used to be guaranteed at the Bernabeu for more than another 180 minutes. Real's remaining home Liga match, in a fortnight, may not draw an animated audience at all, if Barcelona have beaten Atletico Madrid next weekend to secure the championship. Which leaves just the Champions League semifinal second leg against Juventus on Thursday.
That will begin with captains' greetings between the top two goalkeepers of the 21st century, a pair of World-Cup winners. Gianluigi Buffon and Casillas have a combined age of 70, and stand as examples not only of long-term standard-setting but of a capacity to bounce back.
A little over two years ago, Buffon, then 35, had time brutally called on his career by Franz Beckenbauer. Bayern Munich's honorary president had just watched Bayern eliminate Juventus from the Champions League, and took the Italian goalkeeper's sluggish movement, reacting to a long-range shot from David Alaba, as a sign of terminal decline. "He looks like he's retired already," boomed Beckenbauer.
The remark was widely reported, and noted. Lip-readers should ready themselves, if Juve progress to the Champions League final in Berlin, for the moment Buffon spots Beckenbauer post match.
Casillas has never left Real either. He also experienced a relegation, although it was of the personal kind. Eighteen months after he had captained Spain to the World Cup, less than half a season after skippering Real to the league title, he was dropped by the then club coach Jose Mourinho.
The comeback from the Mourinho snub has not been entirely convincing. Carlo Ancelotti, picking up the post-Mourinho pieces in 2013, promoted Casillas to first choice only for European and domestic cup matches last season.
Casillas lifted the European Cup last May. But coupled with the picture of his collecting yet another major prize is the memory, from the final, of his klutzy dash from his goal-line, in the lead-up to the Atletico Madrid goal that for much of the evening put Real on the losing side. Casillas went to last year's World Cup as Spain's No1, as he has been for 13 years. The national team's plunge from holders to hapless was nowhere more vividly captured than in the pictures of "Saint Iker" scrabbling as Arjen Robben danced around him to score the fifth of the seven goals Spain let in in their opening two matches.
On Sunday, the fans saw Real all but wave goodbye to the Liga title. So Wednesday has a swansong feel for the fallen "Saint Iker". Lip-readers should be alert at the coin toss in case the Real Madrid captain whispers: "Gigi, you go up that end. I've had it with the b******* in row C."
