Llanelli will face Bala Town in the play-off for the Welsh Premier League's final Europa League spot next Saturday.
Jordan Follows scored an extra-time winner to secure a 1-0 victory for Llanelli over ten-man Aberystwyth Town.
Aber had been reduced to ten men in the fifth minute when Michael Walsh was dismissed for a high tackle on Ashley Evans.
Goals from Ian Sheridan and Lee Hunt secured Bala Town's 2-1 win over Prestatyn.
Sheridan had given Colin Caton's side a fourth minute lead before Dave Hayes levelled for the visitors on the half hour.
But two minutes after the interval former Prestatyn striker Hunt scored Bala's winner to secure a play-off final at Stebonheath Park next Saturday.