Fisher took the lead as early as the seventh minute as the ball was crossed to the back post by Michael Smith and met by the run of Steve Watts whose firm downward header found the near corner of the net.
Watts doubled his sides lead in the twenty fourth minute when his diagonal left to right run was found by the midfield and he slotted back across goal and past Masters.
Fisher extended their lead eight minutes into the second half. Leon Woodruffe lost the ball on the edge of the Slough area as he was tackled by Damian Scannell and Smith worked some space to his right and picked his spot low to Masters right and into the corner of the goal.
In a rare Slough attack, Andy Ballard volleyed wide as he connected with a Gareth McCleary cross.
Masters then pulled off two wonderful saves, the first in particular being outstanding, both times from Lenny Piper. The first was cut back and Piper struck the ball well from twelve yards, but Masters got a strong hand to the well hit shot and pushed it over the bar. Shortly after, the keeper dived low to his left to push Piper's shot onto the outside of the post and wide as Slough were hanging on.
It was Damian Scannell's turn to next be denied by a good Masters stop as the forward made a diagonal run to the left side of the box before firing in at Masters near post, but the keeper was well placed to again get a strong hand to the ball.
The Slough keeper was helpless to prevent Fisher's fourth as Anthony Riviere picked up Darron Wilkinson's clearance just outside the area and his effort went through a crowd of bodies into the bottom right corner.
Masters again had to be alert to keep out an effort from sub Charlie Taylor as Slough lost the ball on the right and the young forward cut inside but again found Masters blocking the goal.
Fisher deserved winners and with a semi final first leg on Monday, Slough will have to find away to stop a very potent attack from getting through as easily as they did today if they want to have any chance of retaining their League Cup crown.
Fisher Ath Line up
James Pullen, Chris Piper, Ahmed Dean, Nick Davies, Francis Duku, Charlie Hearn, Anthony Riviere, Michael Smith, Damien Scannell, Steve Watts, Lenny Piper. Subs: Steve West (for Watts), Charlie Taylor (for Scannell), Hamid Barr (for Smith), Tim Clancy, Will Packham