Raphinha (2) and Lamine Yamal struck as Barca won 3-1 to reach the Champions League quarterfinals 4-1 on aggregate.
Flick said afterwards: "I'm happy, of course. They played very well.
"We have to look ahead to the quarter-finals. Yes, it's difficult to win the Champions League, but we hope to achieve it. I'm very happy because Benfica is a fantastic team, I respect the game they played. I knew they would make great transitions.
"We could have scored a couple more goals, but I'm very happy."
On Raphinha declaring Barca "are candidates to win everything", Flick was positive.
"I think it's good that the players think like that. They have confidence, they believe in what they're doing, but my job is to stay calm and look to the next game."
The German also had praise for Pedri after his performance: "He's at 100 percent. It's incredible to see what he does with and without the ball. He's playing in the most suitable position.
"He's the best in the world in his position."
He added: "I'm not saying it's easy, but day after day we get better. Today we were able to show how we can improve. That's what we'll do. We'll show them what was good and what wasn't.
"There's another tough game on Sunday. It's good to always focus on the next game. I love the mentality of the players and, on top of that, they're having fun and there's a wonderful atmosphere."