The 4-1 rout, saw Robert Lewandowski, Lamine Yamal, Raphinha (pen) and Marcus Rashford score on the night. The result saw Barca reach the round of 16.
Flick said afterwards: "I don't know what happened to the others. I was focused on my team. We finished fifth. It was a tough match; they played well in the first half.
"I wasn't very happy at the start of the first half, better in the second. We need to improve.
"We conceded that first goal, we played through the middle when we wanted to play wide. The second half was great.
"I'm very focused on the match, but my feeling is that we have a good connection with the stands. They've supported us, given us positive energy, and that's what we needed."
On the prospect of facing a Premier League team in the next round, Flick added: "The Premier League is the best league in the world, there's a lot of money and they can buy a lot of players, but all the teams that play in the Champions League have a lot of quality."