The Rebels were two goals behind in South Wales on Saturday but goals from Charlie Moone and James Dobson ensured Slough would have a second chance to progress.
This time, Moone and Simon Dunn scored first half goals for a clinical Slough Town side, who had to soak up plenty of pressure from Merthyr during the 90 minutes, particularly in the second half.
Both sides made a flying start to the match, which set the tone for an open first 45 minutes. A good spell of Slough pressure ended with the returning Mark Nisbet heading a corner over, and then the visitors almost went ahead as early as the third minute, but Mark Scott – who played the entire match despite suffering with illness – made a good stop from Elliot Richards.
Slough took the lead somewhat against the run of play with 17 minutes played, Moone notching his 11th goal of the season from a Lewis Putman cross. Putman, playing on the right in place of the injured Warren Harris, did well to beat his man and cross low on his less favoured right foot, and Moone showed great instinct to touch the ball in at the near post.
The game flowed from end to end, with both sides counter-attacking to good effect. Dunn put a shot wide from 25 yards but Merthyr were enjoying a lot of possession in the Slough half, forcing corner after corner. The Welsh side fashioned a great chance for Keyon Reffell, who was played clean through on goal by Kayne McLaggon, but his touch was a little too heavy and Scott rushed out of his goal to save with his feet.
Reffell again showed his electric pace with 39 minutes gone as he took the ball 60 yards up the pitch following a Slough corner, but Scott again saved.
That proved to be crucial as Slough doubled their lead on the stroke of half time with a superbly worked goal. Elijah Adebayo combined with Dunn, who played the ball down the right for Sean Fraser to whip in a cross which Dunn powerfully side-footed home after making a clever run into the box.
Merthyr emerged from the dressing room determined to get back into the game and had a positive opening ten minutes, applying a great deal of pressure without being able to break the Rebels down.
The visitors dominated possession for much of the half and were frustrated time and again by the offside flag, with McLaggon in particular appearing to be very unlucky on one occasion.
Sloppy play almost led to Slough sealing the game with a third goal as goalkeeper Oliver Davies’ poor throw out was straight to Lee Togwell. The midfielder tried to lob the keeper from 30 yards, but Davies got back to claw the ball away. Slough maintained pressure from the resulting corner, with Guy Hollis having a free header blocked.
Minutes later, Merthyr missed perhaps their best chance of the half. Reffell picked up Davies’ long clearance and played it to Richards, whose powerful dipping shot appeared to have the beating of Scott, but the keeper did well to keep it out.
Merthyr grew increasingly frustrated with time running out, but Slough stuck to their task superbly and saw the game out, denying the visitors any more clear chances.
Merthyr Town Line up
Oliver Davies, Scott Tancock, Scott Barrow, Ashley Evans (c), Curtis McDonald, Gethin Jones, Elliot Richards (Corey Jenkins), Jarrad Wright, Kayne McLaggon, Keyon Reffell, Ian Traylor (Curtis Hutson). Sub not used: Ben Watkins.