The teenager eased PSG nerves with an unstoppable 77th-minute strike to put the champions back in front after the hosts had battled back from two-goals down and then hit the crossbar.
Mbappe brought down a high ball and without breaking stride, belted a shot into the roof of the net.
With seconds remaining, however, Mbappe reacted to a late challenge from Teji Savanier and shoved the Nimes midfielder to the floor. Referee Jerome Brisard, who booked Mbappe for kicking the ball away in the first half, brought out his red card. Savanier was also sent off.
The teenager said he had no regrets after his sending-off and claimed he would not hesitate to do the same thing again.
The 19-year-old striker’s reaction was in retaliation after he had been scythed down by Savanier
“No, no, no,” said Mbappe afterwards when asked if he wished he had not responded the way he did.
“If I had to do it again, I would and I would apologise to all the supporters and to everyone.
“I cannot tolerate that sort of gesture, it doesn’t belong on a football field. It wouldn’t be a problem if he intended to play the ball, but he made no attempt to play the ball, we all saw it.
“But it doesn’t matter, I’ll go and defend myself before the disciplinary committee.”
Mbappe will now be automatically suspended for PSG’s next game, a home match against Saint-Etienne on September 14 that precedes a trip to Liverpool in the Champions League.
But the nature of the offence means he could face a lengthier ban from domestic action.
Prior to that, Neymar had opened the scoring and Angel Di Maria doubled the PSG lead by scoring direct from a corner.
But Nimes responded in the second half and Antonin Bobichon halved their deficit before Savanier equalised from the penalty spot in the 71st-minute after a spot-kick awarded with the assistance of VAR.
It was Mbappe’s 77th-minute goal that punctured the home side’s hopes, before Edinson Cavani secured the win late on to leave PSG with maximum points after four games of the Ligue 1 season.
Asked if he doubted that PSG would win all three points, Mbappe said: “No, we want to be a great team, and a great team must learn never to doubt itself, even in difficulty. We were in a lot of difficulty today but we come away with the victory.”
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