The 1-3 result lifted Gunners two places up to ninth on 37 points from 26 games while the Foxes stay third on 49 points after suffering a second setback in three days following their Europa League elimination.
Brendan Rodgers’ side took a sixth-minute lead against Arsenal as Youri Tielemans cut inside the area from the right flank and fired a low shot into the far corner.
Mikel Arteta’s side equalised in the 39th when David Luiz headed a Willian cross into the bottom right corner and Lacazette turned the tide in first-half stoppage time as he drilled in a penalty after a VAR check showed Wilfred Ndidi had handled the ball in the area.
Harvey Barnes was carried off five minutes into the second half after appearing to injure his knee stretching for the ball.
Jonny Evans soon followed.
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Poor defending cost Leicester again in the 52nd minute as they allowed the visitors to break through the middle before Willian slipped the ball to Pepe and the Ivorian forward tucked it into an empty net from two metres.