Lens beat Ligue 1 leaders Paris St Germain 3-1 on Sunday to give the champions their first league loss of the season, narrowing the gap at the top between the two teams.
PSG were without Neymar, who was suspended after getting sent off against Strasbourg on Wednesday, and Lionel Messi who is continuing his post-World Cup recovery.
The result means Christophe Galtier's side are on 44 points from 17 games, four points ahead of Lens in second.
The hosts took an early lead after five minutes when a deflection from PSG keeper Gianluigi Donnarumma went to an unmarked Przemyslaw Frankowski, who volleyed the ball into the open net.
Hugo Ekitike equalised for PSG three minutes later when the striker reached a cross before Lens goalkeeper Brice Samba and tapped the ball in.
Lens striker Lois Openda restored his side's lead in the 28th minute when he got a through ball from Seko Fofana and ran into the box, where he beat defender Marquinhos before finishing into the lower-right corner of the goal.
French forward Alexis Claude-Maurice made it three for Lens two minutes into the second half to seal the win.
Swiatek, Gauff through to Australian Open 2nd Round
Sinner survives tough test, Alcaraz eases through
DP World ILT20 Season 3 kicks off
Amorim sees progress in Man Utd's shootout win at Arsenal
