Simon scored just four days ago in the 3-2 away defeat at Rennes which has now brought is tally in the league to three in 21 appearances.
He netted in the 68th minute to bring score to 2-1, after Mauro Icardi and Thilo Kehrer had scored on 29 and 57 minutes respectively for PSG.
It was Nantes third consecutive defeat and they are currently 10th on 32 points while PSG remain top on 58 points.
In another Ligue 1 game on Tuesday, Lille made it back-to-back wins as they pip visiting Rennes 1-0.
Victor Osimhen was in action for 90 minutes but could not get on the score sheet.
He netted the winner in the 2-1 away victory against Strasbourg on Saturday.
Former Chelsea forward Loic Remy got the only goal just four minutes into the game.