Smith's early strike caught out the visitors, with the striker firing across Glyn Garner and into the far corner to give Slough the lead.
But Cirencester reacted positively and stamped their authority on the game. Jake Somerville needed to be alert to keep out a headed effort from Aidan Bennett, but was powerless to stop Nat Jarvis equalising on 16 minutes.
Cirencester had won a penalty kick after referee John Hollier spotted a handball offence, but Somerville dived to his right to make a fine save from Jarvis' effort. However, within sixty seconds, Jarvis had made amends with a cool finish past Somerville and into the bottom corner, as Slough failed to clear.
Nine minutes later, the visitors took the lead, and never looked back from that point. Ed Williams swung in a corner, and Gethin Jones sent a bullet header past the helpless Somerville.
It could have been three minutes later, but Guy Hollis cleared off the line from Jarvis, and Brad Hooper shot over the bar when well placed.
The second half was a similar story to the first, with Cirencester dominating the play. The visitors created a number of half chances, with Bennett shooting wide after a good move, and Williams firing straight at Somerville after running at the heart of the Slough defence. Substitute Josh Parsons also shot off target with plenty of time to weigh up his effort on the edge of the Slough box.
Slough barely got within 20 yards of the Cirencester goal in the second half, and in fact failed to have another shot at goal or corner kick since Smith’s early goal.
Billy Jeffreys joined Smith and Johnnie Dyer in attack in the closing minutes, but never threatened Garner’s goal, and the Gloucestershire side closed out the game very comfortably with Slough unable to make any impact on the game.
Cirencester Town Line up
Glyn Garner, Ian Herring, Ellis Dunton, Mark Pritchett (c), Matt Liddiard, Gethin Jones, Brad Hooper, James Mortimer-Jones, Nat Jarvis, Aidan Bennett, Ed Williams. Subs: Josh Parsons, Ben Proctor, Kyle Pitts, Leigh Henry, Jacob Davidge.