Keys will now take on Munster A in the final and after crushing the hopes of full timers Cornish Pirates, they will travel to Ireland confident of another upset.
Cross Keys fully deserved their victory, every player tackling themselves to a standstill while the pack hunted like mongrels at the breakdown while the backs looked dangerous and full of intent when they got the ball in their hands.
Keys raced into a 10-point lead through Steffan Jones' boot and the opportunism of Kristian Baller on the wing.
A further Jones pot increased the woes for the Pirates as they struggled to get into the match. Rob Cook banged over three penalties for the visitors and the pack earned a penalty try when Keys were down to 14 men.
The Priates hauled themselves back to level terms with another Cook penalty but the elusive Baller dotted down for his second try and even though Cook reduced the gap moments later the Gwent side battened down the hatches to secure a famous victory.
Scorers: Cross Keys: Tries: Baller 2; Cons: Jones 2; Pens: Jones 2
Cornish Pirates: Tries: Penalty; Cons: Cook; Pens: Cook 3
Cross Keys 15 G. David 14 K. Baller 13 L. Andrews (21 L. Williams 57mins) 12 P. Williams 11 N. Trowbridge 10 S. Jones (20 O. Jones 80mins) 9 R. Dyer 1 R. Cornock (18 C. Gould 20-24, 80mins) 17 G. Price 3 M. Jones 4 D. Hodge 5 T. Lampard (16 L. Rawlins 60mins) 6 R. Peebles (19 C. Trayhern 68mins) 7 R. Nash (capt) 8 J. Groves
Cornish Pirates 15 R. Cook 14 D. Doherty (21 T. Kessell 78mins) 13 A. Suniula 12 S. Hill 11 M. Evans 10 C. Thomas 9 G. Cattle (capt) 8 K. Marriott (20 B. Maidment 64mins) 7 P. Burgess 6 C. Morgan 5 M. Myerscough 4 L. McGlone (19 M. Smith 64mins) 3 A. Paver 2 R. Elloway (17 D. Ward ht) 1 R. Storer (C. Rimmer ht)