Flick was full of praise for the Brazilian's contribution up front.
"When I plan the match I do think he can be the best nine. He's very good: his intensity, the goal he scored and the dynamism he has," Flick said.
The head coach felt his side should have been more clinical in front of goal despite the win.
"We have an idea of playing more offensively. We had a great game with a lot of chances, but we only scored two goals. Sometimes you have to be a bit calmer and play a bit more for others," he said.
Flick also praised his side's growing tactical control on the ball, crediting the training ground work behind it.
"I think the most important thing is the training we do, the quality we have in the sessions. How we do the rondos, the small-sided games... they're doing it very well and we're seeing that later in the matches. But there are still situations we can improve, especially when we lose the ball," he said.
Asked about comparisons between Julián Álvarez and Raphinha, Flick turned the question into praise for his Barcelona squad's collective mentality.
"For me, it doesn't matter what position he plays. He shows total commitment to the club and the team. The fans connect with him too. There are other players involved like that, like Eric and Pedri... that's what we need. Players who don't worry about themselves but about others," Flick said, though he declined to be drawn on Atlético Madrid's forward directly.
"I don't want to talk about this. He's not our player. We've won the second match, and I'm happy," he said.
Terzić, whose Athletic Club side leave Camp Nou without a point from their opening two fixtures, struck a defiant tone despite the result.
"From the start we showed an intense performance and played well. We lacked finishing. We weren't very clinical the times we managed to break their line on counterattacks. Defensively I'm happy with most of the actions we had. It's a match we can build on," he said.
The Athletic coach was candid about the pressure of a winless start.
"As a coach I'm aware that football is a results business and I'm responsible for the players' performances. If I could change the situation I'd like to have six points. I try to win constantly and tomorrow I'll get up aiming for three points in the next match.
"I trust this team a lot because I see them working and I'm sure we're going to turn the results around in our favour," he said, before identifying the second half as the turning point.
"In the first half we were able to win the ball back better, and in the second they took control of it away from us. We chased it for so long... and when we had it we lost it again. That was the big difference compared to the first half."
Asked about a refereeing decision involving Yuri, Terzić added: "My answer wouldn't change anything. If five days after the match you're still talking about the referees, something isn't right. If there's been a mistake twice, that's already a pattern. I hope we all learn from this."