Hemel were left pinned in their own half for the majority of the first half as Slough made their intentions known early into the game.
The Rebels came close to taking the lead within three minutes as Matt Lench’s header struck the crossbar, then the follow up from Johnny Goddard was sent wide.
Slough were again denied a goal, as this time Lee Togwell’s header was denied by a brilliant close range save from Craig King.
The visitors scored against the run of play as Ogo Obi lashed his effort into the top right corner in the 32nd minute.
Slough continued to put on the pressure in the second half as Matt Lench crossed the ball towards George Wells, who headed effort struck the side netting.
Hemel Hempstead continued to be a threat on the counter throughout the second half.
And they doubled their lead from a counter-attack thanks to a dangerous cross being delivered by the back post, where Bayley Brown headed it home.
Hemel Hempstead Town Line up
Craig King, Charlie Barkeri, Jernade Meade, Godfrey Poku, Jack Westbrook, Kory Roberts, Josh Castiglione (Bayley Brown 74), Dominic Morgan-Griffiths, Jordan Greenidge (Josh Lelan 84), Ogo Obi (Dara Dada 74), Brooklyn Ilunga. Unused substitutes: Ryan Hope, Luke Holness.