Marseille went top of Ligue 1 on Friday despite throwing away an early lead to draw 1-1 away to a Nantes side who played more than 80 minutes down to 10 men.
The outlook seemed bleak for Nantes when they had Bastien Meupiyou sent off in the ninth minute for pulling down Sarr and denying the Marseille player a clear run at goal.
It was a nightmare moment for the 17-year-old Meupiyou on his senior debut for Nantes.
However the home side drew level six minutes before half-time as Egyptian international Mostafa Mohamed controlled the ball in the box with his back to goal before swivelling to volley in on the turn.
Nantes remain without a win this season while Marseille are unbeaten after four games and are a point clear of Monaco at the top of the standings ahead of the rest of the weekend's matches.
Monaco entertain Lens on Saturday, while reigning champions Paris Saint-Germain visit Lyon on Sunday.