Hansi Flick fumed at Barcelona's defending in their enthralling 4-4 draw with Atletico Madrid in their Copa del Rey semi-final first leg on Tuesday. 

Barcelona bounced back from two early goals to lead at the break, with Pedri, Pau Cubarsi and Inigo Martinez on target for the hosts. 

Robert Lewandowski added Barcelona's fourth 16 minutes from time, only for quickfire goals from Marcos Llorente and Alexander Sorloth to seal a dramatic draw.

Barcelona had the better of the tie, registering an expected goals of 3.59 from their 16 shots compared to Atletico's 1.51 from their 10 attempts at goal. 

But Flick was left furious at full-time, suggesting it was unacceptable for a club like Barcelona to concede four goals, saying his side needs to learn how to close out games properly moving forward. 

"I have warned the players not to concede any chances," Flick told Spanish public television TVE. "I'm disappointed with the result because it was good to see how we managed to fight back after conceding two goals early and, even after we opened a 4-2 lead, we created a lot of chances.

"But it was all in vain because in the last few minutes we let them back into it. We had chances to go to the second leg with an advantage. We will have to talk a lot in the changing room about the goals we conceded. We have to correct the mistakes.

"The team is very young, there is a lot of room for improvement, but that is no excuse. They scored four goals against us, and it's just too much for our standards."

Flick, however, complemented Atletico for their fighting spirit during the clash at the Camp Nou, but did have words of praise for his players after the thrilling clash. 

The Barcelona head coach lauded his side's attack, with Raphinha the standout having created more chances (four) than anyone on the pitch on Tuesday. 

"I am frustrated but still happy with many things I saw in the game. But the conceded goals can't happen," Flick said.

"Atletico played very well, we faced a good and strong team that left it all out there.

"But I think we dominated the game for 80 minutes, but in the last few minutes we didn't defend well. I couldn't believe the fourth goal.

"At least, I think the fans enjoyed it because it was a battle. Atletico have a fantastic team. The important thing is for the team to have confidence moving forward.

"We have to be positive, we are not throwing in the towel, and we are confident we will be able to win the second leg."

Barcelona return to LaLiga action against Real Sociedad on Sunday, with their opponents taking on Real Madrid in the other Copa del Rey semi-final on Wednesday.