Ger Farragher did most to inspire a Castlegar side trying to end the club’s 29-year famine back to their 17th and last Galway title.
The former All Star hit 0-13 from frees in a flawless performance, scoring three in succession to haul the champions back in the closing five minutes after Conor Cooney had blasted a penalty to the net.
The sides were level eight times, with Castlegar leading by 0-10 to 0-9 at the interval and Farragher’s accuracy saw them pull 0-14 to 0-11 in front five minutes after the restart.
All Star David Burke and his younger brother, Eanna, did most to get St Thomas’ moving, picking off 0-7 from play between them in the second half for a side who had never reached the Galway final until last year.
David Burke edged St Thomas in front entering the final quarter before Farragher and Darragh Burke exchanged frees and then Kevin Brady’s fourth point for Castlegar levelled the match with 11 minutes left.
Conor Cooney pointed before blasting a penalty to the net and while Enda Concannon and three Farragher placed ball efforts once more tied proceedings, St Thomas finished strongly with Eanna Burke edging them ahead in stoppage time before his Galway minor team-mate Shane Cooney wrapped up the win with a fine goal.
Scorers for St. Thomas: C Cooney (1-6, 1-2 frees); David Burke, E Burke (0-4 each), S Cooney (1-0); Darragh Burke (0-2, 0-2 frees), D Cooney, K Burke, A Kelly (0-1 each).
Scorers for Castlegar: G Farragher (0-13, 0-13 frees), K Brady (0-4), E Concannon (0-2), T Mannion, D Higgins (0-1 each).
ST THOMAS: P Skehill; C Burke, Robert Murray, D Cooney; E Tannion, Darragh Burke, S Burke; K Burke, David Burke; E Burke, C Cooney, B Burke; S Cooney, Richard Murray, A Kelly.
Subs: D Sherry for D Cooney (36); J Regan for Robert Murray (44).
CASTLEGAR: J Connor; O Teagle, P O’Connell, P O’Flynn; T Mannion, K Keane, D McGreal; G Farragher, B Harnett; D Higgins, E Concannon, D O’Gorman; J O’Gorman, R O’Flynn, K Brady.
Subs: S Connolly for Harnett (39).
Referee: A Kelly.