But it was the introduction of substitute Jamie Molyneux that swung the game in the home side’s favour after Truro had edged a cagey opening half.
The midfielder tormented the visitors with a series of powerful runs down the left and capped a fine cameo display by setting up the final goal for teenager Cameron Young – his first for the club.
Omari Sterling-James and Ashley Sammons went close early on for the Reds before giant Truro defender Arron Pugh had a header blocked in front of goal.
With Jim Mutton outstanding at the back, Truro chances were few and far between after the break and the Reds dominated the chances.
Four minutes into the half Sam Youngs forced a good save from visiting keeper Grant Fisher before Sammons levelled the scores on 62 minutes with a shot from just outside the box that found the bottom left-hand corner.
It was Youngs who headed United into a 71st minute lead, his ten-yard effort from a corner creeping through the legs of the City keeper.
There was a scare for the home side six minutes from time when Ben Watson sneaked in behind the defence but keeper Sam Hornby denied him with a brave block.
Young joined the fray as a late Redditch substitute and rounded the scoring off deep in injury time, tucking the ball home after Molyneux’s shot was parried by Fisher.
Reds: Hornby 7, Williams 6, Caines 7, Oshungbure 8 (Loveridge 73), Flanagan 6, MUTTON 8, Youngs 7, Bridgwater 7 (Molyneux 46, 7), Sterling-James 6, Sammons 6, Ahenkorah 5 (Young 89). Subs (not used): McDonald, Catlow.