The champions, who needed only a point at the Stade Pierre Mauroy to clinch a second successive league crown, were comprehensively beaten by the team in second place, with PSG transfer target Nicolas Pepe amongst the scorers on a famous night for Lille.
The result marked a record defeat for the club under their Qatari ownership, which took charge of the club in 2011.
The champions fell behind after just seven minutes when Thomas Meunier put through his own goal.
Juan Bernat equalized soon after for Thomas Tuchel’s title-chasing visitors, but the wheels began to fall off for PSG when skipper Thiago Silva was forced off injured, to be replaced by Thilo Kehrer.
And things got worse for Tuchel when Meunier also had his evening ended before the break. Moussa Diaby was brought on in his place.
The champions’ horror first half was compounded when goalscorer Bernat was
The second half brought no respite. PSG fell behind shortly after the break when transfer target Pepe broke away to give the hosts the lead, as the champions were made to pay for their first-half travails against the team in second place.
Jonathan Bamba made it 3-1 with 25 minutes left to play, and Gabriel headed home Lille's fourth minutes later to further compound the champions' misery
Portugal defender Jose Fonte thumped home a header to make it five and round off the humiliation.
Pepe scored against the champions during a 2-1 defeat at the Parc
As well as disrupting their
The loss is PSG's worst Ligue 1 defeat since a 5-1 loss to Sedan in December 2000.
PSG's next chance to wrap up what is surely still an inevitable title will come away against Nantes on Wednesday.