The greatest miss of all was by Stephen Moloney for Castletown just before the break when he bore down on goal but somehow managed to shoot wide.
Castletown, with the wind behind them in the second-half, had the greater share of the play but found it difficult to score mainly due to the tight marking that applied to defenders in general, and their own inaccuracy.
Jamie Crean levelled the score on 0-4 each within five minutes of play resuming, but Castletown then scored four on the trot, two from Ryan Murphy, and a point each by Mark Halpin and Seán Roche.
Glynn-barntown suffered a blow when Jamie Crean kicked a close-in free wide to add to their mounting tally of misses.
Team captain Jimmer Doyle, having received from Aaron Kehoe, split the posts for an excellent point with six minutes to go, and when Kehoe himself scored another point from a free three minutes later it left just two between them (0-8 to 0-6).
Castletown's Mark Halpin then made his presence felt with a high kicked point from far out.
In a last-gasp effort to equalise, Glynn-barntown centre-back Murtagh Joyce raced upfield with the ball but his shot at goal was well blocked close to the line, and alert corner-forward Aaron Kehoe was in like a flash to kick the rebound to the net as the game entered injury time.
With the score then at 0-9 to 1-6 the whistle sounded, so extra-time was required in an effort to separate them.
The only scores in the first period came from the Castletown midfield pairing of Seán Roche (free) and Gavin Stamp. Ian Moran had a goal chance for Glynn-barntown but his attempt was blocked.
Castletown showed their authority in the final ten-minute period when Roche pointed another free, and Stamp set up Ross Bealin for a point from play, before Mark Halpin blasted a rasping kick to the net seconds before the final sound of referee Noel Whelan's whistle.
Secretary of the organising committee, Fintan Whyte, presented the cup to Castletown captain, Conor Cleary, after the game amid great jubilation, and joint Treasurer Monica Ferguson presented Gavin Stamp with the man of the match award.