PSG had already qualified from Group C, but Blanc still declared himself unhappy with the showing from his players.
"I am disappointed with the performance of my team in the second half," he told reporters. "It is the second half where we had a problem.
"We lacked a bit of ambition and Benfica played [well]. For what they created in the second half they deserved the win. There has, of course, been lessons, both individually and collectively.
"Hopefully PSG will be able to win the Champions League but before that there will be plenty of games to play."
PSG are currently top of Ligue 1.