The visitors went ahead at the start of the second half when Nuhiu’s effort was deflected past James Shea from close range.
Luton should have levelled as Justin picked out Luke Berry, who was denied by the legs of Dawson.
Shea did well to prevent Reach making it 2-0, while substitute Dan Potts almost equalised but his left-footer was parried behind by Dawson.
Luton again came agonisingly close to levelling with 13 minutes to go, Collins diverting Sonny Bradley’s header on to the post with the goal gaping.
Bradley’s header was then nodded off the line by Nuhiu as Luton’s cup dreams were ended for another season.