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The deadlock was broken six minutes before the break as the 23-year-old tucked a shot into the bottom corner to put the hosts ahead.
Right on the stroke of half time, Lacazette doubled his side's lead after connecting with a precise cross by Yoann Gourcuff.
The former Milan man attempted to claim a goal of his own just after the restart, but his strike when bearing down on goal was efficiently blocked.
The match ball, however, would belong to Lacazette, who completed his hat-trick with six minutes left in the game with another low shot past Vincent Enyeama.