A battling second-half display by the Hatters saw them repeat the 2-1 victory they chalked up on their last visit to Nene Park 18 months ago.
Luton were reduced to ten men for the final 46 minutes of this LDV Vans Trophy tie and looked certain to be overrun given the inexperienced nature of their line-up.
But they survived a barrage of pressure from Diamonds to survive the handicap of the dismissal of defender Sol Davis a minute before half time.
Davis was given his marching orders for second yellow after a foul on Rodney Jack, who had hauled Diamonds back into this tie after Luton shot into an early 2-0 lead.
They went in front in the eighth minute, Enoch Showunmi picked up on a defensive error and bore down on goal before beating Paul Evans for his first senior strike.
It was 2-0 from the penalty spot nine minutes later after Showunmi was brought down by John Dempster and Michael Leary sent Evans the wrong way from the spot.
Jack reduced the arrears with an acrobatic volley six minutes later and for a while it seemed as though the floodgates would open.
Hatters goalkeeper Dean Brill performed heroics to deny Paul Kitson as he dashed clear in the 38th minute and Andy Burgess showed great skill on the edge of the box before firing wide just before the break.
Brill kept up his super show after half time, denying Ritchie Hanlon when he was set free, as Diamonds were unable to cash in on their numerical advantage.