Just 3 days after memorable 4-1 win over Bayern Munich, Barca produced another fantastic match and put 4 more past the hosts in Madrid.
Barca wasn't at its recent best in the first half, although it played its increasingly famous offside trap to great effect to catch out Kylian Mbappe and keep the scoreline all square going down the tunnel for the interval.
In the second half, however, the Catalans pulled off another demolition job like that seen performed at Bayern Munich's expense in the Champions League on Wednesday, with Robert Lewandowski scoring twice in 141 seconds ahead of further goals from wingers Lamine Yamal and Raphinha.
With his team now six points clear at the top of La Liga, Flick admitted that his latest impressive victory "wasn't easy, but we defended very well".
"At half time we made a change, we adjusted some things, especially with the ball. In the second half we had more control of possession. We have to continue in this direction," the German demanded at his post-match press conference.
"Without a doubt, how much we have worked on the defensive aspect is one of the key points. We have invested many hours in working on how to press and defend. It was very important to do well because we knew that they were going to leave spaces," he further explained.
Reminding us that he's "always said" how happy he is to work at Barca and to live in Barcelona, Flick complimented his men for playing a "fantastic game".
"I'm very proud of the team and that all the players worked one hundred percent. I'm also very happy for Inaki Peña, who kept a clean sheet and was very good," Flick said.