Lyon now have 45 points from 21 games but second-placed Olympique de Marseille will move within one point on Sunday if they beat En Avant Guingamp.
Also on Sunday, third-placed St Etienne, who are six points off the pace, travel to Stade Rennais with fourth-placed Paris St Germain hosting Evian Thonon Gaillard.
PSG will welcome back forwards Ezequiel Lavezzi and Edinson Cavani, who are back in the squad after being left out by coach Laurent Blanc for three games for coming late from the December break.
Monaco cemented fifth place on 36 points on Saturday after Bernardo Silva's goal gave them a 1-0 home win over Nantes.
At Lens, Lyon took the lead in the 22nd minute when Nabil Fekir's cross from the left took a deflection off centre back Jean-Philippe Gbamin's heel.
The Lens defensive woes continued four minutes later when fullback Boubacar Sylla handled the ball in the box, allowing Lacazette to double the visitors' tally from the penalty spot.
It was the league's leading scorer Lacazette's 20th goal of the season after the France striker had netted consecutive doubles in his four previous matches.
Lens shifted to a three-man defence in the second half but they remained toothless up front and further exposed themselves to counter attacks.
They stay 19th in the table with 19 points, one point adrift of the safety zone.
(Reporting by Julien Pretot, editing by Pritha Sarkar and Ian Chadband)
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