Despite the result, it wasn't all plain sailing for the Reds, who were under the cosh for spells of the game from an Everton side fighting relegation.
Garna was the primary difference maker though, winning two penalties during the first half, for fouls by James Tarkowski and Ben Godfrey.
Bruno Fernandes tucked the first into Jordan Pickford's bottom left-hand corner, before Marcus Rashford stepped up for the second and sent the ball into the opposite side of the net.
United had further opportunities to increase our lead, with Garnacho firing wide twice in the second half when played in by Bruno Fernandes.