Barca struck all four of their goals on Sunday before halftime - though Flick insisted afterwards the match was more difficult than the scoreline suggested.
He beamed afterwards: "It's fantastic for the fans and the players. Real Madrid has a great team, but we managed to come back from 2-0 down. And after the game in Milan, with 120 minutes, it wasn't easy.
"It's easy to say if you score four... fine... let them score three. We have to improve a lot in defence. When we press everything is fine, but if you make a mistake, especially on the first goal, it gets complicated.
"The team makes very good collective decisions. It's not an excuse, but it's not easy to correct these things in training when playing every three days. We're already thinking about how to improve these things."
These players just love football
Flick admits he'd like to see his players' defending improve given how close Real ran them, despite scoring four times.
He said, "I'm always positive. It wasn't easy, but the team has the power to come back, and it's fantastic.
"Managing the entire team isn't easy, but this squad has a fantastic spirit. They love playing, training, competing... And if they have intensity in training, it's easier in the game."
He added, "We have a fantastic staff around the players. If you want someone with the idea of playing Barça's style, you have to make good decisions. There were good contributions from the bench today, and that's how we have to operate."