It was a highly competitive Cup tie throughout and referee James Jones had to be alert from the outset with two yellow cards and a red shown.
Neath made most of the running in the first half and, after Keys took the lead through a penalty by outside-half Dorian Jones, the home side's positive approach was rewarded with the opening try through winger Bowdy Davies.
Davies ought to have scored earlier but centre Ryan Evans' delayed scoring pass was ruled forward. In the face of the Neath charge, Keys sought to gain control through their well-established kicking game which serves them so well, Jones, Leon Andrews and Gareth David all gaining telling distance.
Keys nudged ahead with a penalty by Jones but Neath countered with a similar score from centre Dean Cummins. Neath outside-half David Langdon really ought to have extended their lead when he received an inside pass from impressive No.8 Steffan Jones but lost the ball with the line at his mercy.
In what was becoming a tit-for-tat battle, Dorian Jones, watched by father and Russia coach Kingsley, landed his third penalty before Langdon gave Neath a well-deserved 11-9 lead at the interval.
As soon as the second-half started, Rob Nash went to the bin and with the match nicely poised, the result hinged on a quickly-taken penalty by 18 year old Neath scrum-half Luc Jones. As he arrowed towards the try-line, Jones was taken out by Rhys Dyer and referee Jones had no option but to dismiss the Cross Keys scrum half.
Neath bravely opted for touch and from the ensuing close-range lineout, a pre-planned move saw Jones getting the touchdown as justice was done.
Keys tried to counter through their forwards but Neath were in the boss seat. A fourth penalty for the visitors by Dean Gunter made it 16-12 but Neath quickly restored their advantage when Langdon dropped a neat goal.
In a stirring finale, Keys threw everything at Neath but the home defence, with full back Aaron Bramwell a commanding figure, was solid and held firm to the end as last year's winners were knocked out.