Garde slated his players for taking their eye off the ball after taking the lead through Alexandre Lacazette in the 53rd minute.
"At 1-0, we stopped playing," Ligue1.com quotes Garde as saying. "We thought we'd done the hard work and had the three points in the bag.
"I tried to encourage my team to keep the same philosophy. I thought that we had to try and score again rather than just sit on our lead. I don't have a team that can do that, and you saw that today.
"Honestly, PSG are in a different league to us. We will try to hang on in there as long as possible, but we must not only look forward. Our objective is to finish in the top three, and we have some serious rivals."
Lyon host Lille at the Stade de Gerland next Sunday.