Robert Lewandowski scored twice in three minutes as La Liga leaders Barcelona thrashed Real Madrid in El Clasico to move six points clear of their rivals.
Real were looking to extend their run of unbeaten games to 43 in the league, which would have equalled the record set by Barcelona between April 2017 and May 2018.
But their hopes of doing that were quashed by a devastating second-half display by their opponents at the Bernabeu.
"It's a hard moment, a tough moment when you lose a game, [especially after] so many unbeaten," said Madrid coach Carlo Ancelotti.
After a goalless first half, Lewandowski broke the deadlock in the 54th minute with a clinical finish from Marc Casado's through ball.
The Poland striker then stunned the hosts with a second, heading Alejandro Balde's cross into the right corner.
Lewandowski had two good chances to complete a hat-trick, hitting the woodwork from the first before firing over from a good position.
Spanish teenage star Lamine Yamal, 17, got Barcelona's third when he drove into the top corner from an angle, with his goal making him the youngest-ever scorer in El Clasico.
Raphinha then lobbed a fourth late on for his first goal against Real Madrid.
The result ensured Kylian Mbappe's first taste of the famous fixture ended in defeat with the France striker having had two goals disallowed for offside and also been denied by Inaki Pena in the Barcelona goal.
Veteran Lewandowski leads youthful Barcelona on title charge
Barcelona finished 10 points behind Real Madrid in La Liga last season, and they are putting their faith in mostly young players to bring success this term.
That approach is so far being being rewarded, with Hansi Flick's team having won 10 and lost just one of their league games so far.
Yamal is arguably their brightest young star but there are others, with Casado and Balde, both 21, getting assists on Saturday evening.
Six players who started the game for Barcelona came through their famed youth academy, but guiding the youngsters from the front is the old-stager Lewandowski.
The Polish striker is 36 but age is not slowing him down, with this double taking his La Liga tally this season to 14 goals in 11 games.
A confident blend of youth and experience proved too much for Real Madrid, who were blown away by their rivals' devastating second-half display.
The visitors also played a high defensive line well to frustrate their opponents, who were caught offside numerous times.
"We always play with the back four very high," Flick said. "It looks dangerous - but it's not dangerous."
Mbappe's frustrating first Clasico
Mbappe, who joined Real Madrid in the summer, had faced Barcelona before while at Paris St-Germain.
He notably hit a hat-trick against them in a 4-1 win at the Nou Camp in the Champions League in February 2021.
But he was unable to replicate that devastating display in this match as he ended up frustrated numerous times when attempting to beat the offside trap.
By his exceptionally high standards, Mbappe has had a slow start to life in Spain, having scored six goals in La Liga so far. He failed to score in his first three league games.
But Mbappe is not alone in struggling for peak form, with this another game without a goal for Jude Bellingham.
The England international scored 19 league goals in a sensational first La Liga season last term, but he has yet to get off the mark in the current campaign.
"We played a first half with intensity. We could have scored [but] we lacked some accuracy," added Ancelotti.
"When they scored they hit two goals that took all of our energy away. We took more risks at the back and they found a lot more chances on the counter-attack.
"For 60 minutes we competed very well and we have to forget the last 30."
BDST: 0842 HRS, OCT 27, 2024
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