Match ends, Barcelona 5, Real Madrid 1.
Luis Suarez scored a hat-trick as Barcelona outclassed Real Madrid to seal a stylish El Clasico victory that further damages their bitter rivals and Madrid's stricken manager Julen Lopetegui.
The former Spain boss now seems certain to lose his job in the wake of a humiliating defeat in a match crucial to his chances of survival.
His side conjured something of a revival in the second half but ultimately they were sunk by an irresistible Barca performance, and it now appears only a question of when he will be fired.
Philippe Coutinho slotted in and Suarez converted a penalty, awarded by a video assistant referee decision for Raphael Varane's foul on the Uruguayan, for Barca's half-time advantage.
Marcelo chested down and finished to give Real hope, but Suarez's header and chipped finish, followed by Arturo Vidal's header, completed the rout.
The visitors had begun the day within four points of Barca, but now trail them by seven and find themselves ninth in the table after 10 matches.
Ernesto Valverde's side, winners of seven league titles from the past 10, are top of the league, leading Atletico Madrid by two points.
European champions Real began the post-Zinedine Zidane and Cristiano Ronaldo era impressively under former Spain boss Lopetegui, but since then the mood has shifted dramatically.
Before Sunday's match, everyone, except those with any official connection to Real Madrid that is, was saying the same thing: Lopetegui was set for the sack and only a handsome win in El Clasico could save him.
Even then the consensus seemed to be that only a wide victory margin - a 5-1, for example - would do the job.
In the second half, his side might easily have drawn themselves level on more than one occasion but luck did not run their way.
Winners of the past three Champions Leagues, they were looking desperately short on confidence, but emerged from the break transformed and almost dragged themselves level in a 10-minute spell of clear superiority.
First Marcelo poked home from close range after good work by Isco and substitute Lucas Vazquez down the right, before Luka Modric clipped the inside of the post and Karim Benzema missed with a header.
That period of dominance was reminiscent of the 1-0 defeat at CSKA Moscow in the Champions League where they had 23 shots at goal and hit the post twice, and last weekend's 2-1 home defeat by Levante, where they had 33 shots, hit the woodwork three times and had a goal ruled out by the video assistant referee.
But ultimately, none of this will count in Lopetegui's favour. Madrid have now failed to win in their past five La Liga games, drawing once and losing four, their worst run since May 2009 under Juande Ramos, who lost six in a row at the end of the 2008-09 season.
In the absence of Lionel Messi, the question was who would be Barca's talisman? Ousmane Dembele, the £135.5m France international forward? Or Coutinho, signed for £142m?
In the end it was Suarez who stole the show and defined this classic Clasico encounter in the Argentine's absence.
His second goal was perhaps the most vital to his side, as it restored a two-goal cushion following significant Real Madrid pressure, but his third, Barcelona's fourth of the night, was by far the most stylish.
The former Liverpool striker dinked a wonderful chip over Thibaut Courtois with Real Madrid ragged at the back.
It seemed to mark the point of humiliation that Barca's fans behind Courtois' goal had been dreaming of, and the reaction in the stands matched that of the players on the pitch: sheer glee as they watched their rivals suffer.
Late substitute Vidal's header provided the final painful blow, and Dembele even came close to adding a sixth in injury time. The European champions had simply crumbled. And who, now, can suggest Lopetegui is the man to rebuild them?
Match ends, Barcelona 5, Real Madrid 1.
Second Half ends, Barcelona 5, Real Madrid 1.
Attempt missed. Karim Benzema (Real Madrid) left footed shot from the left side of the box is close, but misses to the right. Assisted by Mariano with a through ball.
Offside, Barcelona. Gerard Piqué tries a through ball, but Nélson Semedo is caught offside.
Attempt saved. Luis Suárez (Barcelona) right footed shot from the centre of the box is saved in the centre of the goal. Assisted by Sergi Roberto.
Goal! Barcelona 5, Real Madrid 1. Arturo Vidal (Barcelona) header from very close range to the centre of the goal. Assisted by Ousmane Dembélé with a cross.
Foul by Sergi Roberto (Barcelona).
Toni Kroos (Real Madrid) wins a free kick in the defensive half.
Nélson Semedo (Barcelona) wins a free kick on the right wing.
Foul by Isco (Real Madrid).
Substitution, Barcelona. Arturo Vidal replaces Arthur.
Goal! Barcelona 4, Real Madrid 1. Luis Suárez (Barcelona) right footed shot from the right side of the box to the centre of the goal. Assisted by Sergi Roberto.
Attempt missed. Marco Asensio (Real Madrid) left footed shot from the left side of the box is close, but misses to the left. Assisted by Karim Benzema.
Substitution, Real Madrid. Mariano replaces Marcelo because of an injury.
Attempt saved. Sergi Roberto (Barcelona) header from the centre of the box is saved in the bottom right corner. Assisted by Luis Suárez.
Foul by Jordi Alba (Barcelona).
Lucas Vázquez (Real Madrid) wins a free kick on the right wing.
Substitution, Real Madrid. Marco Asensio replaces Gareth Bale.
Luis Suárez (Barcelona) is shown the yellow card for a bad foul.
Foul by Luis Suárez (Barcelona).
Nacho (Real Madrid) wins a free kick in the defensive half.
Goal! Barcelona 3, Real Madrid 1. Luis Suárez (Barcelona) header from the centre of the box to the top right corner. Assisted by Sergi Roberto.
Substitution, Barcelona. Ousmane Dembélé replaces Coutinho.
Foul by Luis Suárez (Barcelona).
Casemiro (Real Madrid) wins a free kick in the defensive half.
Offside, Real Madrid. Toni Kroos tries a through ball, but Karim Benzema is caught offside.
Substitution, Barcelona. Nélson Semedo replaces Rafinha.
Attempt missed. Karim Benzema (Real Madrid) header from the centre of the box is just a bit too high. Assisted by Lucas Vázquez with a cross.
Corner, Barcelona. Conceded by Lucas Vázquez.
Foul by Rafinha (Barcelona).
Toni Kroos (Real Madrid) wins a free kick in the defensive half.
Corner, Barcelona. Conceded by Sergio Ramos.
Attempt blocked. Jordi Alba (Barcelona) left footed shot from the centre of the box is blocked. Assisted by Coutinho.
Offside, Barcelona. Sergio Busquets tries a through ball, but Luis Suárez is caught offside.
Offside, Real Madrid. Toni Kroos tries a through ball, but Isco is caught offside.
Attempt missed. Luis Suárez (Barcelona) right footed shot from the centre of the box is close, but misses to the right. Assisted by Sergi Roberto.
Luis Suárez (Barcelona) wins a free kick in the defensive half.
Foul by Casemiro (Real Madrid).
Ivan Rakitic (Barcelona) wins a free kick in the defensive half.
Foul by Isco (Real Madrid).