Jack McKnight’s coolly-taken spot kick early in the second half proved to be the difference between the two sides at Grosvenor Vale.
The Stones generally had the better of the first 45 minutes, but Slough had a number of opportunities to open the scoring.
Smith twice went close for the hosts, firing just wide on the half hour mark after winning the ball and carrying it into the box, and then on 40 minutes he rattled the crossbar from 25 yards.
Slough broke away immediately and Josh Jackman forced a save from Wealdstone goalkeeper Isted after being played in on goal.
On the stroke of half time, Ben Harris headed a corner into the path of Sam Togwell, but the Rebels skipper could only head over the bar from close range.
Slough made four changes at the break with Fraser, Kuhl, Ben Harris and Hodges replaced by McKnight, Worsfold, Okorogheye and a trialist.
And just a few minutes in, Warren Harris – playing as a striker – was fouled in the penalty area by Wealdstone defender Cawley. McKnight stepped up and notched his second goal of pre-season, sending Isted the wrong way.
Okorogheye was close to grabbing a first goal for the senior team, but Isted made a fine reaction save to keep his volley out.
Worsfold was a threat down the left side for Slough, and on 69 minutes he lost his marker but blasted over the bar from a tight angle.
Next up for Slough is an Emirates FA Cup Second Round Qualifying tie at Dartford next Saturday, as the 2020/21 season gets underway.
Slough Town Line up
Jack Turner, Josh Jackman, Louis Lomas, Sam Togwell (c), Matthew Lench, Ben Harris, Warren Harris, Aaron Kuhl, Sean Fraser, Ryan Bird, Paul Hodges. Substitutes (all used): Lee Togwell, Max Worsfold, Ada Okorogheye, Trialist, Jack McKnight.