Arles claimed their only away win of the Ligue 1 season as these two already-relegated sides played out a poor contest at Stade Felix Bollaert.
Yann Kermorgant got the only goal of the game for the bottom side, for whom this was only a third victory from their 37 league games to date this term.
Lens will also make the drop down a division and there had been calls from some supporters' groups for fans to boycott this game as a protest at the club's plight, although there was a crowd of over 28,000 in attendance.
They also look set to see manager Laszlo Boloni depart for pastures new after failing with the survival mission he was tasked with when he arrived in January.
The hosts had two great chances take the lead, with Eduardo forcing an excellent save from Vincent Plante with a dipping volley.
Zakarya Bergdich then teed up the striker in the 35th minute but his header hit the bar,
And those missed proved costly as Kermogant powerfully headed home from Camel Meriem's corner two minutes before the break.
The same two players almost combined to double the away side's advantage after 51 minutes.
Meriem was again the provider as his free-kick found Kermogant, but Lens keeper Hamdi Kasraoui made an athletic save to push the ball round the post.
The keeper then denied a Kermogant volley, again from a Meriem free-kick, as the pressure increased on the hosts.
Lens managed to fashion a late chance to find a leveller but substitute Yohan Demont fired inches wide.