La Liga and European champions Real Madrid were rocked by a much-transformed Barcelona side that handed them a 4-0 thrashing in the season's first El Clasico Saturday.
Going into the match at the Santiago Bernabeu, however, Real were confident they could undo Barcelona's rapid revival under Hansi Flick. They had every reason to be.
The reigning Spanish and European champions had gone 42 matches unbeaten in the league, one short of the all-time record held by their arch-rivals.
They flexed their muscles in midweek, thrashing Borussia Dortmund 5-2 in the Champions League with a sensational second-half display in which Vinicius Junior – who is tipped to win the Ballon d'Or on Monday – scored a hat trick.
And this summer Madrid finally signed the player they craved for years, French superstar Kylian Mbappe, a devastating attacking threat seemingly destined to elevate them to an even higher plane.
That was President Florentino Perez's dream. Mbappe's too.
The hotly anticipated Clasico, Mbappe's first, was the perfect stage for him and Madrid to put Barcelona in their place.
Flick's tactical approach, featuring an extremely high defensive line, also seemed ripe for Mbappe and Vinicius to pillage with their pace.
However, Los Blancos were caught out time and time again by Barcelona's supremely well-drilled offside trap and were ultimately dismantled in the same way they had anticipated beating their opponent.
Shockwaves
Robert Lewandowski's brace early in the second half stunned the Bernabeu and Lamine Yamal and Raphinha's strikes on the counterattack helped Barcelona to a sensational 4-0 triumph to move six points clear at the top of La Liga.
The victory sent shockwaves through the capital and caused Madrid fans and media to launch an inquisition of their team.
Mbappe, who had two goals disallowed for offside, cut an extremely frustrated figure and is yet to settle at the club.
The forward has six league goals this season in contrast to Lewandowski's 14.
"The star's first Clasico was a cataclysm – a failure, stumbling eight times in Flick's offside trap. Shrunken and without venom, he's a worry," wrote Madrid newspaper AS.
"Kylian Mbappe will not keep fond memories of his first Clasico with Real Madrid, instead he will try to turn the page as quickly as possible," added Marca.
"The goal was getting smaller and smaller for Kylian, and he could not find a way of beating (Barca goalkeeper) Inaki Pena."
Despite Ancelotti insisting Mbappe was "calm" ahead of the game, recent events may have taken a toll.
He is wrangling with former club Paris Saint-Germain over millions in back pay and was criticized in his homeland after not playing for France in recent Nations League fixtures.
Swedish media reported he is being investigated over an alleged rape in Stockholm following a trip there during the international break. Mbappe has dismissed the reports as "fake news."
'Don't have to bin everything'
Ancelotti insisted his team had not been sent back to square one.
"I liked the first half, we have to follow that line," said the coach.
"We don't have to throw everything in the bin, we just have to forget the last 30 minutes – we can't give up, we just have to learn.
"We came out of the last defeat well and we have to do the same, I am certain we will do better."
Madrid last lost in La Liga over a year ago, against Atletico Madrid, and Ancelotti tinkered with his set-up afterward, giving Jude Bellingham a hybrid role.
The England international had started the season up front and scored 10 goals in his first 10 games, but later helped shield the team defensively on the left.
This season Ancelotti has moved Bellingham out of attack to accommodate Mbappe, but has not yet found a permanent home for the midfielder.
Without the creativity and wisdom of Toni Kroos, who retired this summer, Madrid have been wildly inconsistent.
Fede Valverde has inherited Kroos's No. 8 shirt but despite taking a central role this season is struggling to set the tempo of matches.
Mbappe might be more comfortable playing off the left flank, where he thrived at PSG, but that is also Vinicius's favorite position.
Ancelotti has plenty to chew over in the weeks ahead while trying to ensure Barcelona do not race out of sight.