PSG took the lead through Zlatan Ibrahimovic early in the match but wasted a huge number of chances in the ensuing 20 minutes, with the Swede hitting the post from point-blank range and seeing a penalty saved, while Lucas Moura missed a one-on-one.
Reims bounced back to take a shock 2-1 lead into half-time and, even though PSG clawed a goal back through Ibrahimovic, they saw two further efforts cleared off the line in the dying minutes to deny them maximum points.
Blanc says that his only criticism was that his side failed to kill the game in the first half but maintains that they played some impressive football despite having had a relatively short pre-season.
"I can only repeat that PSG are not quite ready in their preparations and we saw that tonight," he told BeIn Sport after the match.
"Paradoxically, I remember my team playing very good football, creating a countless number of chances.
"The only criticism I have for my players - and I told them this - is that we failed to kill the game.
"We are lacking a little preparation. I expected to have some difficulties. The result isn't there but the performance was encouraging for the future."