They looked in deep trouble with almost half an hour gone, trailing 1-0 and reduced to ten men when Tom Bennett got a red card in the 25th minute for his second bookable foul.
Martin Carruthers, making his debut on loan from Lincoln, seemed to have given Cambridge the edge, but a 29th minute breakaway transformed the match.
Chris Beardsley ran through a dithering defence to score an unlikely equaliser and inspire his depleted team to outfight the home side.
Cambridge were never able to regain the initiative, and it was the Harriers who grabbed the lead in the 61st minute when John Mullins rammed home a header from a pinpoint centre from Billy Jones.
Luke Guttridge hit the post for desperate Cambridge, but as they threw men forward Harriers took advantage to clinch the points four minutes from time.
Ian Foster and Blair Sturrock combined to set up Gary Birch who stabbed the ball in to send the three hundred travelling fans wild.
Cambridge probably had more of the play, but it was the Harriers determination to win the ball in vital areas which gave them the victory which keeps them in touch as Cambridge are cut adrift at the bottom.
Cambridge boss Steve Thompson gambled on fitness to send out one of the most experienced sides Cambridge have managed to field during the last couple of seasons, but his plan backfired after his team lost their grip towards the end of the first half.
Ten man Kidderminster were the ones expected to tire in the last third of the game but they had the spirit to keep going as Carruthers and Guttridge, big influences early on, faded out.
Harriers were much tighter in defence once they had the lead in sharp contrast to a Cambridge side who showed only too clearly why they had managed only three wins during the campaign.