An own goal from Jorge Saenz in the second-half earned Barca the 1-0 win.
Flick said afterwards: "It was a very tough and very important match. I'm very proud of what my team has done these past few weeks and months."
"What stands out above all is the commitment of each player."
"Of course. The three points are very good for us. It's perfect. Sometimes you can think that games are like Dortmund, Atlético... but no. There are very tough games like today's. I'm very proud of the team and, above all, of how they defended. Iñigo Martínez's performance was perfect.
"It wasn't easy to play fast. We said we had to adapt to the positions and maintain possession. In the end, the important thing was the mentality to fight until the end."
Barca are now seven points ahead of Real Madrid and Flick also said: "Tomorrow they're playing. But what we're doing is looking at ourselves. Right now we're focused on recovering. I always tell the players that the important thing is to recover.
"We'll arrive in Barcelona at dawn, recover tomorrow, and then fly to Dortmund on Monday. But there are no excuses; we're just focused on the pitch."
He added, "Everyone has taken a step forward. We suffered at the beginning of November, and after the Christmas break, everything was different. The key was the defeat against Atlético. We lost but played very well, and with that confidence, we started the year. The players need more recovery, but we can't control that."