City had taken the lead in the first half through Phil Foden before Richarlison notched an equaliser for the Toffees.
But Mahrez grabbed the game by the scruff of the neck and regained the advantage with his curling effort.
The Algerian international took it first time and watched it bend past a helpless Jordan Pickford, who couldn’t reach it.
Mahrez then wheeled away in celebration while telling his teammates to keep calm.
Fans have reacted to the strike and they think it could be one of the 29-year-old’s best efforts of the season so far.
Bernardo Silva would go on to add a third for City and give them a two goal advantage.
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