The Gwent club had already knocked Cardiff out by 3-0 in an earlier round but this time they left it until injury-time before defeating gallant Corus of Division Two West.
The lead had changed hands four times with Corus leading 17-16, when Brynmawr ran the ball out from their own line and wing Richard Dennington scored at the other end for a 23-17 victory.
Cross Keys stunned holders Llanelli by leading 31-0 at the interval and ran out 38-14 winners. Keys will now be hoping for a fourth successive home draw in the quarter-finals.
Caerphilly led North Wales club Llangefni 37-7 at the break, but the minnows would not lie down and played excellent rugby to score three tries, though the Cheeesemen scored eight themselves in a 54-21 win.
Bridgend disposed of Blackwood by 53-15 and a 9-0 try-count as the vistors landed five penalty goals, while Aberavon defeated Bonymaen 25-16 in a match where the losers ran in two late tries.
In an all-Premier clash Pontypridd gained a good 22-11 win at Bedwas with the home side's only try coming from former Pontypridd Youth wing Stefan Sankala. Neath also went through, but struggled to win 15-5 at Whitland with the Welsh All-Blacks tries coming from former Bonymaen forwards Steve Phillips and Andy Llewellyn.
Ebbw Vale were due to meet Swansea next Saturday at Eugene Cross Park in a league match, but instead will now meet in the cup.
Konica Minolta Cup Round 6.
Aberavon 25 Bonymaen 16
Bedwas 11 Pontypridd 22
Bridgend 53 Blackwood 15
Caerphilly 54 Llangefni 21
Corus 17 Brynmawr 23
Cross Keys 38 Llanelli 14
Ebbw Vale v Swansea (postponed)
Whitland 5 Neath 15
Full roundup to follow