The hosts made 209-5 before bowling out their opponents for 146 with around five overs remaining.
Tom Westley did most of the damage with the bat for Essex thanks to a mammoth knock of 105 off 57 balls, while Ravi Bopara (23), James Foster (36 not out) and Ryan ten Doeschate (37) also did their bit at the crease.
Mitchell Claydon took two wickets for Kent, who struggled to combat Essex's dynamic batting lineup.
Sam Northeast (41) top-scored for the Spitfires when it was their turn out in the middle, but a lack of runs at the top of the order saw them fall short.
Jesse Ryder gave an impressive display with the ball, taking five wickets for the loss of 27 runs to help his team continue their strong campaign.