With 79 minutes gone the depleted Wrens looked out of sight at 5-0 down to a fast moving Nailers outfit eager to avenge a 4-1 loss at Kirklington Road a couple of weeks earlier.
Indeed it could have been worse but for a great penalty save by Cameron Smith
But by the 83rd minute it was 5-3 as Rainworth suddenly found a new lease of life with goals fromLiam Theakstone, Sam Dockwray
and Jake Walker.
And, had home keeper Ryan Hopkiss not saved well from Dockwray's 85th minute free kick when it might have been 5-4, then who knows what would have happened in the last five minutes.
Joint manager Ady Smith
began up front in preference to leading scorer Theakstone, who is due to play in a county schools competition final tomorrow and so began as the Wrens' only substitute.
A lively Belper outfit grabbed a 23rd minute lead which, it must be said, had been coming, when Sam Vickers found the net with a low drive from the edge of the box.
Three minutes later Cameron Smith
could not hold a by-line cross and Ashley Hunter struck the second.
It remained at 2-0 until four minutes of the second half when Hunter struck again.
Justice was done when Smith saved Hunter's harshly awarded penalty, but Ben Bowring (58) and Luke Robinson (65) made it 5-0.
Rainworth looked dead and buried until the 79th minute when Theakstone, on for skipper Lewis Wilson, rounded off a move through the middle.
A minute later Sam Ward
cut in from the right, looked on in agony when his shot hit the bar, and then despair turned to joy when Dockwray hammered home the rebound.
The away following could hardly believe it when Ward and Theakstone combined to set up Walker for the Wrens' third.
But there was to be no fairy tale as Hopkins held onto Dockwray's blistering 85th minute free kick.
BELPER: Hopkins, Crossley (Bailey 68), Rushby (Parkin 71), cartwright, Worthington, Robinson, Seluam, Bowring, Baker, Hunter, Vixkers (Wheatcroft 75).
RAINWORTH: c. Smith, Helmkay, Henderson, Wilson (Theaksone 49), Harris, Dowdall, Ward, Dockwray, A. Smith, Blakeley, Walker.
REFEREE: Richard Eley of Derby.
WRENS MAN OF THE MATCH: Sam Ward