Paul Wilkerson had looked all set to become Slough's hero as he saved Stuart Whittaker's second-half penalty to earn Slough an extra half hour, after the teams had been level at 1-1 after 90 minutes.
The goalkeeper guessed right, yet was fortunate to be still on the field after only being cautioned for bringing down Graeme Tomlinson in the 58th minute incident.
Three divisions and 66 league placings separate these teams, but the parity they enjoyed 18 months ago in the Football Conference was reflected in a tight opening period.
Macclesfield, who had to rally from two goals down at the Moss Road 10 days previously to force this replay, struck first. Ben Sedgemore arrived late to head in Steve Hitchen's cross after Wilkerson failed to find distance on his clearance.
The boggy conditions, which necessitated a pre-match pitch inspection, proved influential as the Macclesfield keeper, Ryan Price, also struggled to kick away back-passes.
After the lively Bryan Hammatt had sidefooted one such clearance wide, Justin Channing collected another on 15 minutes and crossed for Kenny Hughes to sidefoot a left-footed volley into the top corner.
Slough Town Line Up
- 1 Paul Wilkerson
- 2 Justin Channing 15
- 3 Kenny Hughes
- 4 Graham Roberts 12
- 5 Richard Peirson
- 6 Michael Thorp
- 7 Eddie Denton
- 8 Graham Kemp 16
- 9 Andrew Deaner
- 10 Brian Hammatt
- 11 Steve Browne
Macclesfield Town Line up
Price, Hitchen, Ingram, Tinson (Lonergan 112), Wood, Sodje, Askey, Sorvel, Tomlinson, Sedgemore (Griffiths 84), Whittaker (Howarth 95). Subs not used: Clyde, Davenport.