After suffering their heaviest league defeat in 19 years, 2018 FIFA World Cup victor Kylian Mbappe hit out at his Paris Saint-Germain teammates, saying the Ligue 1 giants played like debutants and lacked personality.
Bernat was sent off later in the half in controversial circumstances and PSG would capitulate in the second 45 minutes.
However, the Spanish full-back was shown a straight red card shortly before the break when he brought down Pepe as the striker was rushing towards goal.
Second half goals from Nicolas Pépé, Jonathan Bamba, Gabriel dos Santos Magalhaes and Jose Fonte gave Lille a resounding victory.
Christophe Galtier's side went 2-1 up six minutes into the second half when Pepe beat the offside trap to score from close range. You can't let in three, four or five, " Mbappe told Canal Plus television.
"You can lose, but you must lose in a certain manner - we cannot lack character like we did here", said the France global.
"That said, losses happen, but we must play with more personality - it is one of our biggest failings".
"We've still got six matches left and we need to win at least three or four to be assured of the Champions League next season".
"We will be 13 or 14 players short".
PSG played the match with a number of notable absentees, including Neymar, Edinson Cavani and Angel Di Maria.
But Tuchel took umbrage to the comments after the match and has since played down suggestions of any psychological shortcomings from his squad, instead commenting that he was forced to utilise "sick players who should not have played".
"Even [Moussa] Diaby and [Thilo] Kehrer could not play I do not know who can play in Nantes!".
"With 10 players it became complicated, we played with sick players who should not have played".
They fell behind after just seven minutes when Thomas Meunier put the ball in his own net. "To win here, we would have needed more quality". Everyone sees that. And I will tell that to the president, yes.
Earlier, Saint-Etienne kept the pressure on Lyon and Marseille in the race for third spot with a 3-0 home win against Bordeaux.