Cavani, signed from Serie A side Napoli back in July, scored the winner on Wednesday in the closing stages of extra-time after the holders had earlier levelled as former PSG striker Mevlut Erding cancelled out the Uruguayan's 24th-minute opener.
The brace made it 18 goals for the 26-year-old forward since his move to the Parc des Princes and Blanc was quick to single out Cavani for a fine performance.
"Cavani played a great game," Blanc said.
"He had everything in his game. He fought as always.
"Technically, I think he played a very, very good match, And, like any striker, it has to be finished by goals, and then he scores both."
The win marked PSG's first in five matches against Saint-Etienne.
Blanc was delighted to see his side end their barren run against Christophe Galtier's men as they eye triumph in a competition the capital club last won in 2008.
"There was much joy in the dressing room," Blanc added.
"They (the players) really wanted to beat this team.
"The Coupe de la Ligue is a target, perhaps not the most important, but it is a goal.
"I had no feeling of revenge. It is not just PSG who have struggled against them.
"This is one of the good teams in the league. They are hard to beat, but they have been beaten."
