Two weeks after coming off the bench to score twice against Guingamp, he bailed out PSG with an unstoppable 77th-minute strike to make it 3-2 after Nimes clawed back from 2-0 down and then hit the crossbar.
Striker Edinson Cavani added a fourth in injury time after being set up by winger Angel Di Maria, who earlier scored direct from a corner.
With seconds remaining, Mbappe reacted to a late challenge from midfielder Teji Savanier and shoved the player forcefully to the ground.
Referee Jerome Brisard, who showed Mbappe a yellow card for petulantly kicking the ball away in the first half, instantly brandished a red.
Mbappe stomped off, looking unhappy, but the 19-year-old star of France's World Cup-winning campaign was berated by his own goalkeeper Alphonse Areola for his wild reaction. Savanier was also sent off.
In the first half, Di Maria spotted a gap inside the near post and expertly curled the ball in from the left corner flag for 2-0. Moments earlier, Neymar tapped in right back Thomas Meunier's cross after 36 minutes.
The Brazilian ran over to a sign in the crowd which depicted him as a 'cry baby' and he sat in front of it and pretended to blubber following his opener.
Two weeks ago, confusing VAR decisions helped PSG win at Guingamp 3-1. In that game, the home side had a goal disallowed by a contentious VAR decision when leading 1-0 and a blatant penalty not reviewed with the score 1-1. This time, VAR did not spare PSG.
PSG seemed to be getting another reprieve when leading 2-1 with 20 minutes remaining. Brisard waved away penalty claims, after Thiago Silva caught the back of midfielder Theo Valls' leg as he turned inside the penalty area.
But he changed his mind after reviewing the images and Savanier equalized from the spot in the 71st, drilling a low shot inside Areola's right post.
Areola was well beaten by midfielder Antonin Bobichon, who struck in the 63rd with a curler from the edge of the area into the top right corner.