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Etienne started the game brightly and they almost took the lead through striker Ricky van Wolfswinkel, who found space for a shot despite the tight angle only to see his effort fly wide.
Lens had not given up the fight, though, and Yoann Touzghar pulled one back for the visitors with the game's second standout goal, this time the frontman taking aim from range to bullet a shot past Ruffier.
The away side soon clawed back level after Kevin Theophile-Catherine produced a handball in his own area, allowing Touzghar to grab a brace by converting from the spot.
Lens then moved ahead with just under 15 minutes to play thanks to Pablo Chavarria, who shot into the top corner following some clever passing from Dimitri Kevin Cavare to make it 3-2.
In a game that continued to swing in both directions, Etienne ensured that they were not to go home red-faced, as Mevlut Erding finished into the top corner in the 83rd minute to leave the final score at 3-3.