The Rebels let a comfortable two goal lead slip away in the final ten minutes as Beaconsfield fought back to level the scores, but were successful with all five of their spot kicks, Ollie Jones crucially seeing his effort saved by Jack Turner who then followed up by tucking away the decisive kick.
Another massive boost for Slough was the debut of Harrison Gilkes after over 13 months on the sidelines with an anterior cruciate ligament injury sustained last summer. Gilkes impressed in the first half before being replaced by Sean Fraser at half time.
Both sides went close in the opening four minutes of this tie – Guy Hollis hitting the angle of post and bar for the Rebels – and later Josh Jackman shot over after linking up well with Warren Harris on the right.
Nathan Smart drilled in a low shot which Jamie Norris dealt with low by his post, but half time arrived with neither side having created much of note.
Slough took the lead seven minutes into the second period with a direct free kick from Matt Lench. Gavin James was chopped down just outside the box, giving Lench the opportunity to get the ball over the defensive wall and past Norris.
The Rebels went on to have much the better of the play and plenty of the ball. Norris turned a strike from Fraser behind, whilst Spencer Bellotti poked the ball just wide after a neat Beaconsfield move.
But Slough added a second on 68 minutes from an unlikely source, as Smart – playing at left-back – moved inside and beat Norris from 25 yards with a fine curling effort.
James was unlucky not to get on the scoresheet, whilst Harris was also denied by the home keeper.
Six minutes remained when former Rebel Lewis Putman won a free kick just outside the Slough box, and the winger stepped up and found the net with a low strike which went under the defensive wall.
And Slough failed to see the game out as, a minute into stoppage time, Turner made a good save only to see Beaconsfield work the ball back into the box, where Luke Neville guided a header into the net.
The tie went to a shootout, and Lench, James, Brad Wadkins and Fraser were all successful for Slough before Turner’s two moments of glory settled the tie.
Beaconsfield Town Line up
Jamie Norris, Callum Mapley, Scott Cousins, Jerome Ecclestone, Luke Neville, Wes Daly (c), Aaron Morgan, Jordan Ajanlekoko, Daniel Brown, Aaron Minhas, Lewis Putman. Substitutes: Mitch Gutteridge, Charlie Kuehn, Ollie Jones, Spencer Bellotti, Kofi Lockhart-Adams.