Now they have equalled that feat after securing their place in today's third round draw following a hard-fought victory at once-proud Penarth. Mike Richards, Jamie Davies and Andrew Bayliss scored the crucial tries for the non-league giant-killers.
Coach Paul Watkins said: "We knew it was going to be hard and it was a very tough game but the players really dug deep and got the result they deserved. I think the boys are learning what it takes to win these big games.Our main aim is to win league status. We've shown we can compete with teams at a higher level. It's a great advert for the club."
Bryncethin will be joined by fellow Districts outfits Cambrian Welfare and Abertysswg also kept their cup dreams alive by battling through the next round.
Tonypandy club Cambrian Welfare from the Rhondda and East Glamorgan District overcame Division Five's Glyncorrwg 29-12 in only their second season in the senior cup thanks to tries from David Owen and Jonathan Davies and the prolific boot of outside-half Julian Huntley.
Club secretary Steve Thomas said: "This was a massive win for the club and we're just going to enjoy every game we get from now on. We've got some great young backs who could give anyone a go in the next round."
Gwent club Abertysswg booked their place in the third round in style with a convincing 34-18 win over struggling Cowbridge. Nathan Pullin scored two tries while prop Jonathan Osbourne, scrum-half Jamie Parry and full-back Brent Jones all followed in the rout.
Backs coach Brian Smith said: "It was a fantastic performance from the boys. We know we're not going to win the cup but it's a great sideline to the league and we'd love to make a name for ourselves by taking a few big scalps."
Dinbych, Caenarfon, Pwllheli and Llangefni, who survived a late fightback by Aberdare, are all flying the flag for north Wales in the third round of the cup following their successes.