"We played two games and it's justified that we're through. I don't want to talk too much about my team, because it wouldn't be fair to Dortmund," said Flick.
"They made our lives very hard but what was important is we made it to the semi-finals."
Through to the Copa del Rey final and four points ahead in LaLiga, Barca remain on track for a treble.
Barca midfielder Fermin Lopez, whose pass led to the Ramy Bensebaini own goal, said the experience would make the Catalans stronger.
"Dortmund have a really good team, you saw that. Last week we made them suffer at our place. We suffered here, but in the end we were able to limit the damage," said the 21-year old.
"We're now in the semi-finals and can draw a lot of strength from this game because it was a big task."
The defeat was Barca's first in any competition in 2025 and Flick said he had "full trust that we'll get back on track".
"Now's the time to celebrate what we've done, getting to the semi-finals, then we can get back to analysing what's ahead of us," added the German.
END/MSS/RH
Comment: