The visitors got off to the dream start when Zuriko Davitashvili was clumsily felled by Remy Cabella in the box and the Georgian kept his cool from the spot to tuck the resultant spot kick into the bottom corner.
Lille seemed almost shell-shocked to concede six minutes into the game and despite dominating the ball, they were sluggish and struggled to create anything in the final third.
The hosts were lucky not to go 2-0 down just before the half-hour mark when Lucas Stassin beautifully picked out Louis Mouton with a deft cross but with the goal at his mercy, the midfielder blazed a half-volley high and wide.
That moment proved to be crucial as the home side stormed up the other end of the field and Jonathan David was dragged down in the area.
Play continued for a long time before VAR advised the referee to review his decision, and after being awarded, the penalty was cheekily chipped down the middle by the Canadian striker to level the score.
Lille couldn’t find a second before the interval, but they made a quick start to the second half when a delightful touch from Hakon Arnar Haraldsson looked like it would set him through on goal, but he was wiped out by Dylan Batubinsika who received a straight red card for his troubles.
The stage was now set for the home onslaught, but Davitashvili could’ve torn up the script as he found himself in on goal, but he went for power and Lucas Chevalier stood tall to make the save.
Yet again, Les Verts would be punished for their profligacy in front of goal as minutes later, David broke free and unselfishly squared the ball for Osame Sahraoui to tap home.
It threatened to turn into a rout in the final 20 minutes when Gabriel Gudmundsson smashed a shot in off the bar before Sahraoui made it four with a delightful finish.
The three points allow Lille to jump back into the top four and only two points behind second spot, while St Etienne remain just one place and one spot above the drop zone with just one win in eight league games.
Les Verts need to turn their form around if they want to avoid the drop. Their next fixture, against relegation rivals Rennes next week will provide the best opportunity to turn their season around.
FlashScore Man of the Match: Jonathan David (Lille)