Ben Harris was twice denied goals by an offside flag in the opening 15 minutes, but Slough were not to be denied as Josh Jackman drilled home from the end of the six yard box just past the half hour mark.
Jackman surprisingly got his name on the scoresheet for a second time just five minutes later, taking a sublime pass from Eitel Goueth before sliding the ball past the goalkeeper.
Moments later, Goueth almost made it three with an attempted chip from 35 yards, but the ball landed just over the bar.
Jonathan North had to make a save at full stretch as the first half came to a close, with Ben Harris also hitting the side netting with a volley from Max Worsfold’s corner.
Into the second period, Tom Derry fired over from 18 yards following more great work from Goueth, and then the midfielder carved out a chance for himself, forcing a save from Kings Langley’s substitute goalkeeper.
Around the hour mark, Scott Davies added a third with a well-struck free kick from 25 yards.
A further goal almost arrived when George Hunt cut inside but saw his shot hit the post, with Derry following up to score, but again from an offside position.
The hosts grabbed a consolation goal from the penalty spot two minutes from time.
Slough Town Line up
First half: Jonathan North, Josh Jackman, Guy Hollis, Lee Togwell, Max Worsfold, Eitel Goueth, Ben Harris, Warren Harris, Aaron Kuhl, Gabe George, Ryan Bird. Second half: Jonathan North, Freddie Grant, Mark Nisbet, Eitel Goueth, George Hunt, Tom Derry, Scott Davies, Sean Fraser, Ryan Bird, Joe Lawal, Paul Hodges.