Record-breaking striker Asa Thomas netted four times as Trearddur eventually eased past Rovers to reach the semi-finals.
Thomas, who set a new North Wales coast senior goal-scoring record the previous weekend when he reached 632 in his career, moved on to 637 and 55 for the 2022-23 season with another outstanding display at Lon Isallt.
After half time arrived with a 0-0 scoreline, Thomas broke the deadlock on 48 minutes thanks to a Tom Scott assist.
It remained 1-0 until the 74th minute, then Thomas added another three in very quick succession, the latter a penalty.
Kaine Bentley and Noel Owen notched further goals before the end.
It took a stunning goal from Luke McKittrick to break Llangoed’s determined resistance in this quarter-final at School Lane.
The scoresheet was blank until the 24th minute when McKittrick ended the stalemate with an unstoppable strike.
Fellow midfielder Ryan Folksman made it 2-0 at half time when he netted from the edge of the box.
The score was unchanged until Bay went goal-crazy in the final 15 minutes.
Rhys Lloyd headed in from a corner before Matt Reynolds notched his 21st goal of the season.
Substitute Bryn Roberts, who came on in the 70th minute, then added a late hat-trick to mark a memorable debut.
Two late strikes from Marquis Holland – the second eight minutes into added time – guided Llanfairpwll into the last four.
Gaerwen had led from the fifth minute when Dino Williams found the net, Alan Mark Owen supplying the assist.
It stayed at 1-0 until the 76th minute when Holland provided the equaliser, Cian Owen setting him up.
It looked like spot-kicks would be needed to decide the winner until Holland struck his 14th goal of the season with 98 on the clock, goalkeeper Rhys Owen with the assist.
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