Both sides created chances in the opening quarter of an hour, but it was the visitors that took the lead when Hemed fired in from close range from a rebound.
Gustavo Cabral immediately tried to put Almeria under pressure down the other end, but his headed finish was kept out by Julian.
Celta saw more of the ball at the start of the second half, and came close to getting back on level terms when Santi Mina picked out Charles with a cross, but his header was kept out by the Almeria keeper.
Celta kept pressing for the equaliser in the final minutes, but a string of attempted crosses from Fabian Orrellana were blocked by the Almeria defence to make sure of the win.
The result lifts Almeria out of the bottom three, moving them up to 16th, while Celta Vigo remain eighth.