Real Madrid coach Carlo Ancelotti was unhappy with how Barcelona's bench celebrated their fourth goal after seeing his side beaten 4-0 in Saturday's Clásico at the Santiago Bernabéu.

Robert Lewandowski scored twice, with Lamine Yamal and Raphinha also finding the net as Barça ended Madrid's 42-game unbeaten streak in LaLiga and moved six points clear of them at the top of the table.

The celebrations after the fourth goal, Raphinha's 10th of the campaign, spilled in front of the Madrid bench with Ancelotti confronting Barça coach Hansi Flick. Ancelotti, though, said his issue was with the behaviour of one of Flick's assistants.

"[The problem] was with the assistant, not with Flick," Ancelotti said in his post-game news conference when asked to clear up what had happened on the touchline.

"The assistant was not a gentleman with the way he celebrated in front of bench. And Flick agreed with us."

Asked about the incident in his news conference, Flick said: "I didn't see it. I just spoke with Carlo and it was something ... it's normal in this situation, when you celebrate a goal maybe it's not ... we're old enough to speak about that."

Madrid had won the last four Clásicos in all competitions and avoiding defeat here would have seen them match Barça's LaLiga record 43-game unbeaten streak.

However, following a goalless first half, they collapsed after the break.

Lewandowski scored twice in three minutes to take his tally to 17 for the campaign in all competitions. Then Yamal, becoming the youngest ever Clásico scorer at 17, and Raphinha completed the rout.

"Until the goal it was an even game," Ancelotti said. "We had chances and could have scored, but we weren't clinical.

"When they score, it saps some energy from you and it becomes another game. They did a lot of damage on the counter.

"I liked the first half, we have to follow that line. We don't have to throw everything away, 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 against Atlético Madrid last season and we have to do the same. I am certain we will do better."

It proved a tough introduction to the Clásico for Kylian Mbappé, who had two goals ruled out for offside and missed a slew of chances.

In total, Mbappé was caught offside eight times -- tied for most in a LaLiga game in the last 15 seasons -- as Los Blancos, who had 12 offsides in total, struggled to get in behind Barça's high line.

"We took risks with his position," Ancelotti added of Mbappé's performance. "They have a high line and due to fine margins we have not been able to take advantage of it.

"He has also had three or four chances and has not taken them when we need a little more.

"The result doesn't reflect what happened on pitch. Barça go ahead and then the confidence that came from that changed the game. We took risks and they're a team in form who were dangerous on the break.

"The defeat worries me but we have to pick ourselves up quickly.

"We have to keep fighting. We're not going to be that far away this season from what we did last season."

The result capped a remarkable week for Barça, coming just four days after they demolished Bayern Munich 4-1 in the Champions League.

Under Flick they have now won 12 out of 14 games in all competitions, but the German coach refused to get carried away.

"We start the journey and we're doing really well," he said. "Like I always say, we have to make things better and we do it also, but today was not easy.

"We keep going with our idea, we have a flow at the moment and we have to keep going.

"I've always said I'm really happy to work for Barça and also to live in Barcelona. It's an amazing job, it's a new part of my life and it feels really good.

"Today we made a fantastic match and I'm really proud about the team. And how we play is very important as well.

"This will give the players more confidence. The celebration in the dressing room was good to see. Now we have a recovery day, then I give the players two days off and after the focus is on Espanyol next weekend."