St Thomas will face Gort in the Galway SHC final after Conor Cooney hit eight points for the 2013 All-Ireland champions, who claimed a 1-15 to 1-10 victory over Loughrea in Athenry.
The losers were too reliant on captain Neil Keary, who scored all but two points of their tally.
St Thomas' led 1-7 to 1-4 at half-time - Brendan Farrell scored their goal - and they have now qualified for their first decider since they got the better of Loughrea in the 2012 final.
Bernard Burke scored an early point for St Thomas' but then Keary shot a goal in the second minute. St Thomas' were more skilful and hit 1-3 without reply in seven minutes. Cooney scored a couple of frees, David Sherry was on target and so was Farrell, who blasted to the net in the 10th minute.
Keary answered that with a point and although Conor Cooney hit back, points from Keary reduced the arrears. But Fintan Burke and Darragh Burke scored as St Thomas' took a 1-7 to 1-4 half-time lead.
Keary scored a free at the start of the second-half but Cooney was very accurate with his frees.
Loughrea had to wait until the 41st minute to get their first score from a player other than Keary, when Gearoid Loughnane made it 1-10 to 1-7. And when Keary added another point three minutes later Loughrea trailed by just two points.
But when the pressure came St Thomas' didn't cave and Cooney, Darragh Burke and Cooney again put the game beyond doubt.
Keary and Darragh Burke traded scores and by the time Emmet Mahony pointed the game was up for Loughrea. And Gerard Kelly delivered the final blow with three minutes left.
In the other semi-final, former Galway minor Gerard O'Donoghue scored the vital goal as Gort beat Craughwell 1-17 to 0-18 in the first of the double-header.