De Jong impressed on the night as Eric Garcia, Robert Lewandowski and Ronald Araujo struck the goals for Barca.
Flick said of the Dutchman afterwards: "He's very important, as is Pedri. In the second half, we had more control and pace, and that made the match more difficult for Oviedo."
Flick then recalled that the team has achieved four consecutive wins without Lamine Yamal: "We made the right decisions, the level has risen. But above all, it shows that we have a fantastic team."
Lewandowski played a key role after coming off the bench, Flick continued: "It's not just eleven players. Whoever comes on has to change the dynamic. Lewandowski did that, not just by scoring, but by helping the group."
Araújo also scored and provided defensive solidity: "It wasn't easy, Oviedo started well. I'm happy with the goal, it's an important step for his confidence. He's doing better than last season. We're testing different central pairings, and having options is positive."
Finally, regarding the match in general, the coach reiterated his playing philosophy: "We believe in playing with the ball. I'm happy with the three points. Lewandowski and De Jong were decisive. We also need to have solutions on set pieces. Joan García's mistake? It's football, it can happen. He's a great goalkeeper and he knew how to react."