Robert Lewandowski scored twice and Lamine Yamal piled on to ruin Kylian Mbappé's first clasico as Barcelona routed Real Madrid 4-0.

The lopsided victory in Spain's capital ended the host's unbeaten run in La Liga at 42 games, one shy of Barcelona's record streak in 2017-18. Carlo Ancelotti's side suffered its first loss since Sept. 23 last year.

And what a loss it was.

Lewandowski got the visitors going from a superb pass by Barcelona's latest youth talent Marc Casadó in the 54th minute and rose up to head in a fine header three minutes later to silence Santiago Bernabeu Stadium.

Yamal made it a rout in the 77th when the teenage phenom rifled a shot from an angle over goalkeeper Andriy Lunin. That goal made him the youngest scorer in a clasico at 17 years, 105 days, surpassing teammate Ansu Fati, who was about 250 days older in October 2020.

Raphinha then broke free with Madrid completely unhinged and chipped Lunin in the 84th.

The win came three days after Barcelona thumped Bayern Munich 4-1 in the Champions League. It has outscored its last five opponents 21-2.

“We came here to do just this,” Yamal said. “We had lots of confidence and when we scored the second goal, we wanted to score a third, and then a fourth, as many goals as possible. To win 4-0 at this ground and beat Bayern 4-1, we showed that we are ready for anything.”

It is an understatement that Mbappé had a frustrating first game against Barcelona in a white shirt.

The France star was caught eight times offside by Barcelona's synchronized back four and failed to beat second-choice goalkeeper Iñaki Peña one-on-one with his team down two goals.

“We knew that they played with a high line, and we just couldn't take advantage of it,” Ancelotti said. “Sometimes (Mbappé) fell offside, but he had three or four chances to score and needed a better finishing touch.”

Hansi Flick, meanwhile, had a night to remember in the first clasico for the German coach.

Barcelona still has financial troubles that cast doubt over its future but its youthful team has made huge steps forward since Flick replaced Barcelona great Xavi Hernández in the summer.

“Today we made a fantastic match and it is all about the team. Everyone gave it 100%," said Flick, who Ancelotti called “a gentleman” for telling his bench to cool it when they effusively celebrated the fourth goal near Madrid's dugout.

After opening a six-point lead over Madrid at the top of La Liga, it is no longer a foregone conclusion that with Mbappé on board Madrid will waltz to a second straight domestic title.

Casadó was one of five homegrown players that Flick put in his starting lineup, the same 11 from the Bayern win. Six players under 22 years old started for Barcelona, led by 17-year-olds Yamal and Pau Cubarsí.

Casadó had flashes of the flawless ball control of a Sergi Busquets as he helped compensate for Madrid's extra man in the midfield before he cued up the game-changing pass to play Lewandowski clear to slot home.

Yamal upstaged Mbappé this summer when Spain beat France en route to winning the European Championship, and he did it again. To top it off, he scored with his supposedly “not as good” right foot before flashing his new braces decorated with Barcelona's colors for the cameras.

Mbappé ensnared by offside trap

Mbappé was ruled offside five times in the first half hour, as Barcelona pressed high. Vinícius Júnior, who featured in a fascinating duel with Cubarsí, missed a golden chance in the 21st when he shot past the post from close.

“When they scored those back-to-back goals it took the energy out of us,” Ancelotti said. “This is a complicated moment for us. It hurts to lose a game and especially after going 42 games unbeaten, but we shouldn't just throw everything away because this team will play better.”

Peña was questioned if he was up to the task of replacing Marc-Andre ter Stegen, out long term with a knee injury. His strong performance, which included two stops to deny Mbappé, was his first great game in goal for Barcelona.

“Our coach said that playing a high defensive line was non-negotiable,” Peña said. “It is risky to play with such a high defense line, but the effort and work of the entire team is reflected in the offside traps we are creating.”

Raphinha's goal confirmed his massive step forward under Flick. The Brazil forward, who acted as Barcelona captain, has 10 goals in this campaign.

Lewandowski's goals 16th and 17th overall for the Poland striker this season, taking his league-best tally to 14. He also hit the post. Mbappé, by comparison, has eight goals in all competitions.

Ayoze strikes again

Ayoze Pérez scored his seventh goal since joining Villarreal this campaign to help it win 2-1 at Valladolid and lift his team into third place.

Rayo Vallecano beat Alaves 1-0 after scoring late despite having played a man down from the 22nd, while Las Palmas beat Girona 1-0.