The first chance of the game arrived when Ryan Newman put Kerry Morgan through on the left, but Jake Somerville came out well to block his shot. Shortly after, Slough almost scored themselves when Johnnie Dyer's header was well parried by Merthyr Tom Bradley before he caught the ball under the bar.
The Rebels, denied the services of a number of players through injury and unavailability, took the lead courtesy of a Jake Parsons strike in the 35th minute, following a neat corner routine. The ball was fired across the area and was met first time by Parsons, who drilled a hard shot along the ground and into the net.
But the hosts turned the game on its head with two quick-fire goals at the beginning of the second half, with Kayne McLaggon equalising and then Kerry Morgan putting the Martyrs ahead.
Merthyr took just three minutes to equalise in the second half. Jarrad Wright embarked on a barnstorming run down the left, beating several Slough players before playing the ball across the face of goal. Somerville got a hand to the ball to turn it away, but McLaggon seized the loose ball and scored from six yards.
Just three minutes later, Morgan robbed a Slough player of possession and took the ball inside to finish well with a shot inside the near post.
Ian Traylor then made it 3-1 on the hour mark as Merthyr made their possession and pressure count. A corner was played to the far side of the area where Wright headed it back across goal for Ian Traylor to head into the net from close range.
Merthyr went close to a fourth when Kris Leek played the ball to McLaggon at the near post, but Slough recovered and Somerville gathered. But the hosts continued to dominate, and Morgan set Ryan Newman up for a super strike which Somerville touched over the bar.
Against the run of play, Billy Jeffreys pulled a goal back in the final minute. Somerville took a long free kick from the half way line and the ball was turned back across the Merthyr area to be bundled into the net by the defender for his first goal for the club, but it was not enough to force extra time, and Slough now turn their attention back to the Southern League, Premier Division, with home games against Hitchin and Chippenham to come.
Merthyr Town Line up
Tom Bradley, Dan Summerfield, Jarrad Wright, Kris Leek, Jamie Rewbury, Ryan Green (c), Kerry Morgan, Gavin Williams, Kayne McLaggon, Ryan Newman, Ian Traylor. Subs: Steve Williams, Giles Cutlan, Matthew Harris, Guillermo Bauza, Corey Jenkins.