The Ligue 1 leaders claimed a 3-1 win at Bordeaux on Tuesday thanks to two late goals to progress to the last four.
Javier Pastore put PSG ahead before a mistake from Adrien Rabiot allowed Andre Poko to hit back for Bordeaux.
But Rabiot made amends with a goal on 86 minutes before Blaise Matuidi sealed the win soon after.
Blanc talked up the importance of reaching the latter stages of the cup, but rued the concentration lapse which cost his side a goal.
"The game is won, yes, but we had a momentary lapse of concentration that cost us dearly as we conceded a goal that put back Bordeaux in the game," he said.
"It is true that we had a good reaction after the goal, which allowed us, with the same player who made the mistake - Adrien Rabiot - to score the second goal, then we scored a third.
"It is often said, our team does not dwell on the result. We always want to try to score goals.
"I think it's interesting. For us it is essential to qualify for the latter stages of the Coupe de la Ligue, it is a good night tonight."
Rabiot said he was delighted to score an important goal after costing his side the equaliser in the 48th minute.
"It was important for me to score that goal because I had made the mistake that cost us for their goal," he said.
"I wouldn't say that is bothered me mentally but I really wanted to make amends for it. I wanted to do it and I did, that was important for me."
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