After Cardiff's victory over Newport by 20-14 on Friday evening, the other three quarter-finals on Saturday saw victories for Llanelli and Pontypridd in the afternoon and Ebbw Vale in the night match.
Wales scrum half Robert Howley had scored the try that took Cardiff to a 20-14 win over holders Newport at the Arms Park and it was Cup kings Llanelli who overcame Bridgend to win by 46-24.
Bridgend struck early with tries by Adrian Durston and Aisea Havili, but Llanelli stormed away in the second half as Ian Boobyer touched down two of their five tries and outside half Stephen Jones kicked 21 points, while former Scarlet, Craig Warlow, notched 14 for Bridgend.
Pontypridd full back Brett Davey kicked five first-half penalties that in the end proved the difference against a game Caerphilly side. Pontypridd won
46-31 with centre Sonny Parker and the Caerphilly forward Andrew Williams both grabbing braces of tries.
A magnificent effort by Pontypool saw them almost add Ebbw Vale to their scalps after having already knocked out Swansea. The Vale won 27-22 thanks to a late try by centre Paul Matthews. Kickers Gareth Cull and Byron Hayward had fought a good duel and Pontypool Park was aflow with a splendid crowd for the evening match.
The draw brought out Pontypridd first and then their opponents, Cardiff, while Llanelli were drawn against Ebbw Vale or Pontypool, but a few hours after the draw it was Ebbw Vale who won through.
DRAW for PRINCIPALITY CUP SEMI-FINALS:
(both to be played at the Millennium Stadium, Cardiff)
LLANELLI vs EBBW VALE 3pm
PONTYPRIDD vs CARDIFF 5.30pm
Pontypridd and Cardiff have met three times in the Cup - Pontypridd won 9-7 home in 1978/79 and 13-6 away in 1979/80, while Cardiff won 8-6 in the 1993/94 semi-final.
Llanelli have beaten Ebbw Vale in all their five previous meetings - 10-4 in the 1975/76 semi-final; 15-9 home in 1979/80; 41-0 home in 1987/88; 19-12 in the 1997/98 final at Bristol and by 38-26 in a 1999/2000 semi-final.
As the countdown continues for RWC2015, Tournament Chief Executive Debbie Jevans visited the Millennium Stadium to discuss preparations for the eight matches and reveal the positive news that 100,000 tickets for games at the home of Welsh rugby have sold in the last seven days.
Jason Harries is targeting a first win on the World Series circuit this season with Wales. The series returns to action this weekend in Dubai where Harries is part of a team hoping to build from its efforts in round one in October.
Wales skipper Jevon Groves says his side have addressed a few points from Gold Coast and aim to 'hit the ground running' in the next two rounds of the World Series, kicking off with this weekend in Dubai before heading off to South Africa next week.
Wales Sevens manager Steff Thomas is hopeful his side can build from a quarter-final spot in the opening round of the World Series in Australia when his side take part in the forthcoming double header in Dubai and South Africa.