Glantaf captain Aled Ward did the damage for the home side, the No. 8 scoring a remarkable four tries to guide his team home. Flanker Charley Smith and wing Aron Cynan were also on the score sheet with fly half Elis R Jones kicking four conversions and a penalty.
Openside flanker Jonnah Cannon claimed a late try for Treorchy but it was Glantaf who came out on top.
It took Ward's side just eight minutes to open the scoring with the skipper diving over after the Glantaf forwards had recycled the ball impressively. Jones converted and it wasn't long before Ward added a second score. Jones once again kicked the extra two and added a penalty soon after as Glantaf moved into a 17-0 lead inside 25 minutes.
At this stage, Treorchy were struggling to implement their attacking game and there was still time before the break for Glantaf to pull further clear. Cynan scooted over in the corner before Ward completed his hat-trick.
If the first half had been all about Ward's individual efforts, the second started in similar fashion. The No. 8 crossed with ease to deny any Treorchy hopes of a comeback. Glantaf crossed twice more for late scores with Cannon gaining a late consolation for the visitors.
St Joseph's followed Glantaf into the last 16 of the Cup with a narrow 10-5 win over Stanwell.
The first half was a very tight affair with the two sides going into the break level after neither broke the deadlock. A few key coaching points by St Joseph's coach Steve Blades saw his pack put in a very strong second half display in awful weather conditions.
Playing into a gale force wind, St Joseph's took the lead with a try after a series of pick and go's. Stanwell fought back with a try of their own but this was to be St Joseph's day. With three minutes left on the clock, Stanwell had a lineout five metres out from their line, but hooker Kian Eley was quick to take advantage to pick up and crash over.