The hosts pulled level with Monaco at the top of the table ahead of their encounter with Nantes, but they left it late against a struggling opponent
Paris Saint-Germain needed a late penalty from Edinson Cavani to secure a win over Nancy and pull level with Monaco at the top.
The Ligue 1 champions were on top for most of the game but were unable to find the net until the 80th minute when Serge Aurier was fouled in the box.
Edinson Cavani scored from the spot to put pressure on his side's rivals, who take on Nantes this week.