Ronaldo's party ruined as Atletico put Real to sword
It has been a sobering fortnight for the leaders of Europe's elite leagues.
Bayern Munich conceded four times in a single game against Wolfsburg. That was a shock, but not a terminal setback.
Chelsea let in four against Bradford City. That was a sensation, but irrelevant to their title bid.
But when Real Madrid, top of La Liga and in a far tighter title race than their German or English equivalents, concede four without reply or even a meaningful shot, the tremors are louder and last longer.
The champions of Europe crept away from the Madrid derby debilitated by Atletico's latest blitz against them.
If Atletico victories over Real no longer count, technically, as shocks - in six meetings this season, Atletico have won four times and drawn twice - a 4-0 scoreline still has the power to resonate.
It was a battering. It was also, if anything, mildly flattering to the losing side. Had Real's Sami Khedira been punished for blocking a shot with his hand in the penalty area, Atletico would have had three goals by half-time.
Contrition is compulsory for the losers in these circumstances, and, by Saturday night, a number of Real players were reminded to avoid being photographed with anything resembling a smile on their faces as they filed into a pre-arranged party at a private venue to celebrate Cristiano Ronaldo's 30th birthday. An unfortunate piece of timing.
Pictures were released of Ronaldo looking as solemn as a man hosting 150 guests can, without appearing sour, while James Rodriguez, Marcelo and Keylor Navas grinned into someone's camera phone before their images were Instagrammed past the control of the bouncers.
None of those three had been involved in the match. Nor had a trio of other senior men.
However, Real's several absences were only a partial alibi for a performance coach Carlo Ancelotti described as the worst of his 18 months in charge.
Ancelotti must plan now without James, who has just undergone surgery, for at least another two months, while defender Sergio Ramos faces approximately six weeks of recuperation.
Marcelo, suspended for Saturday's match, Luka Modric and Pepe should be back sooner.
Madrid miss all of them. Their best football this season has been played by a clearly established first XI, identified since September by Ancelotti and barely rotated when he has them available.
Atletico coach Diego Simeone highlighted his team's "combination play" that undid Real, the passing and the movement.
Simeone values the set-pieces and swift counter-attacks that have been the trademarks of Atletico's rise under his watch, but the Argentinian knows his team need to evolve and have a Plan B and C.
This was not a victory by slam-dunk, via towering headers from corners, but one gained through sustained asphyxiation of Ancelotti's team.
Its roll of honour had plenty of newcomers, too - players added since last season's title.
Atletico lost their best passer, Koke, to injury, inside 10 minutes. His replacement, Saul, aged 20, came on and promptly scored their second goal via a spectacular overhead kick, Tiago having given them the lead seven minutes earlier with a low drive that Iker Casillas should have saved.
Another to shine was left-back Siqueira, who may yet become as influential as Felipe Luis, now of Chelsea, used to be.
There were also goals for Mario Mandzukic and Antoine Griezmann, the strikers brought in to replace Diego Costa. They have 11 goals between them since the Spanish winter break ended.
Meanwhile, Lionel Messi produced another devastating attacking show as Barcelona thumped Athletic Bilbao 5-2 last night to move within a point of Real Madrid.
Messi scored Barca's first goal and played a part in three of the others.
Elsewhere, Carlos Tevez was on target as Juventus swept aside AC Milan 3-1 to complete a Serie A double over their old rivals and move ten points clear at the top.
Arjen Robben scored his 12th goal of the season to help Bayern Munich beat VfB Stuttgart 2-0 - their first win of the year - while Borussia Dortmund hammered Freiburg 3-0 to climb off the bottom of the Bundesliga table.
Bayern winger Arjen Robben notched his 12th league goal this season when he picked up the ball just inside the box and drilled in an unstoppable left-foot shot in the 41st minute for the visitors.
Stuttgart went further behind in the 51st minute when David Alaba curled a spectacular 35-metre free-kick into the top corner of the net.