Second-placed Lens have lost only once in 17 Ligue 1 games this season and are now just four points behind Christophe Galtier’s star-studded league leaders.
Lois Openda scored one goal and set up another for Franck Haise’s side.
PSG were without Neymar, who was suspended after being sent off on Wednesday, and Lionel Messi, who continues his post-World Cup recovery.
The hosts led after five minutes when Przemyslaw Frankowski volleyed into an empty net after a rebound off Italy goalkeeper Gianluigi Donnarumma.
Hugo Ekitike quickly equalised for PSG but Openda beat defender Marquinhos and fired past Donnarumma into the bottom corner to give Lens the lead again in the 28th minute.
Alexis Claude-Maurice added a third two minutes into the second half and – despite Kylian Mbappe playing the full game – the club from northern France held on for a notable victory.
Lens drew with Nice last week on their return to action after the World Cup but have won six of their last eight matches in the league and all nine at home this season.
PSG’s last defeat was a 3-0 loss to Monaco on 20 March, 10 days after they lost in the Champions League to Real Madrid.