In winning their quarter-final tie by 10-9, Munster 'A' exacted revenge for their loss to the Pirates in the inaugural British & Irisih Cup final in 2010.
Leinster 'A' had to call on all their reserves to see off Bristol at the Memorial Stadium and book their place in the last-four.
Tries from Andrew Conway, Andrew Goodman, James Tracy and Fionn Carr, in addition to 10 points from the boot of Noel Reid, helped them to a 30-26 victory.
Munster 'A' won both inteprovincial 'A' team games between the sides this season and beat their rivals 36-29 at the RDS in last year's semi-final.
The following day Bedford Blues take on Newcastle Falcons in an all-English affair at Goldington Road (kick-off 3pm).
Two tries from prolific Wasps-bound winger Josh Bassett inspired a Blues comeback in their quarter-final clash with Llanelli.
Early tries from Kristian Phillips and Nic Reynolds had seen the west Walians take control and a two-point lead into the interval. But the Blues scored the first points of the second half through the boot of Jake Sharp and never looked back.
In addition to Bassett's second try, Sharp went on to kick a total of 22 points in a 32-18 win that keeps the Blues on course to go one better than 2011 when they finished runners-up to Bristol.
To maintain their interest, though, they need to beat a Newcastle side that will be bristling with intent following their first defeat of the season.
Bidding to finish the season unbeaten in both league and cup fare, the Falcons concluded the regular English Championship campaign with a disappointing 19-14 home reverse at the hands of Bristol.
The Falcons had won all 29 matches up to that point including a double over the Blues who they have avoided in the RFU Championship semi-final draw.
A last gasp try from debutant Noah Cato and a pressure kick from Jimmy Gopperth sealed a dramatic victory for Newcastle the last time the sides met at Kingston Park on March 8.
BRITISH & IRISH CUP SEMI-FINALS:
MUNSTER 'A' v LEINSTER 'A', Dooradoyle, Garryowen FC, Friday, April 26, 7.30pm
Bedford Blues v Newcastle Falcons, Goldington Road, Saturday, April 27, 3pm