A depleted Rebels side, missing Ben Harris through injury and four players - Francis Amartey, Matt Lench, Dan Roberts and Billy Clifford - due to them being cup-tied, dictated the majority of the game but lacked the cutting edge required to break through the Marlow defence.
The first half was one-way traffic with Louie Soares going close early on. A misjudgment from Simon Grant, the Marlow goalkeeper, saw the ball nicked off his toes and played to Soares, but the keeper recovered to tip the ball over.
Moments later Soares would have another strike at goal. With the ball sitting up nicely, Soares struck narrowly wide with a thunderous effort which would have been unstoppable had it been on target.
Seconds later Warren Harris was played in behind with a lofted through pass, but he dragged his effort wide of the mark.
Manny Williams would go close twice in the closing stages of the first half, his first effort being tipped over the bar by Grant and the second striking the bar, following up on a George Wells effort.
An early goal in the second half turned the tie on its head. Despite major calls for offside, Bossman was sent through on goal, and the striker rounded Jack Turner to put the hosts a goal ahead.
The Rebels responded, fashioning an excellent chance of their own moments later. Quick one-touch passing found Harris bursting into the penalty area with space to shoot but his effort was saved once again by Grant.
Just moments later Williams would have a shot fly just over the bar following a lucky bounce in Slough’s favour.
Later, a set-piece routine almost came off for the Rebels as the ball was played short to Wells. His effort was well hit but was narrowly wide of Grant’s net.
Ultimately it just was not Slough’s day, and it means the Rebels crash out of the competition at the semi-final stage for the third consecutive season.
Marlow Line up
Simon Grant, Curtis Chapple, Leslie Sackey, Jay Welch, Adam Richards, Louis Rogers, Devontae Romeo, Jordan Edwards, Kelvin Bossman, Isaac Osei-Tutu, Kamaron English. Substitutes: Calam Gallimore, Chris Ovenden, Tristan Campbell, Allen Bossman, Marcus Mealing.