Lacazette turned the ball in from close range with his knee in the 29th minute after midfielder Corentin Tolisso set up the former Arsenal forward with an overhead kick.
Seven-time French champions Lyon moved one place and point above Nice, and one point behind Lille in fourth spot.
Lyon goalkeeper Lucas Perri stopped Saint-Etienne's only genuine chance in the 76th, foiling striker Ibrahim Sissoko in a one-on-one.
The match was halted for several minutes early due to the amount of smoke from flares lit by home fans.
There were no visiting fans allowed because of the risk of clashes. A brutal fight in the centre of Lyon four years ago involving around 150 rival fans led to several injuries.
Earlier Sunday, midfielder Tom Louchet scored six minutes into second-half stoppage time to earn Nice a 2-2 home draw with Lille.
Although Lille extended their unbeaten run to 10 games overall, the northern side wasted the chance to overtake Marseille and move into third place.
Lille took the lead in the 17th minute when 19-year-old Belgian forward Matias Fernandez-Pardo broke free down the left and scored past goalkeeper Marcin Bulka.
Midfielder Sofiane Diop equalised in the 56th with a smart back-heel from close range but Dutch defender Mitchel Bakker restored Lille's advantage 10 minutes later.
With seconds remaining, Bulka joined the Nice attack for a free kick and Louchet pounced with a low shot.
Keito Nakumara and Junya Ito had a goal each as Reims won 3-0 at struggling Le Havre to go seventh and level on points with Nice, who are sixth on goal difference. Striker Oumar Diakité got the other goal.
The match was briefly interrupted after Ito's goal in the 57th when some Le Havre fans made homophobic chants.
After the stadium announcer said the game would be abandoned if the chants continued, they quickly stopped.
Elsewhere, rock-bottom Montpellier won 3-1 at home against Brest.
Arnaud Nordin and Wahbi Khazri scored inside the first 12 minutes.
After Jonas Martin pulled a goal back early in the second half, Nordin's penalty was saved by Marco Bizot, but substitute Tanguy Coulibaly ensured victory with a late goal.
Also on Sunday, Rennes lost 2-0 at home to midtable Toulouse.
Rennes fired coach Julien Stéphan on Thursday and former Argentina coach Jorge Sampaoli, who is expected to be hired, watched the game at Roazhon Park.
Defending champions Paris Saint-Germain are six points ahead of second-place Monaco, with both winning on Saturday.
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