The Uruguayan striker started the fightback after 10-man Les Verts had moved to a two-goal lead at Stade Geoffroy-Guichard, before Blaise Matuidi rescued a 2-2 draw for the champions deep into stoppage time.
Despite dropping points, Cavani insists that not losing was vital as PSG continue to defend their Ligue 1 title.
"It's important to have avoided defeat," Cavani told the club's official website.
"It was a very difficult match and we knew, playing Saint-Etienne away, that it was going to be a tough game.
"Yes, we conceded two goals, but we managed to come back into the match and that's the most important thing tonight."
PSG host Lorient on Friday night.