Auchinleck Talbot stretched their record number of Scottish Junior Cup final wins to nine but needed extra-time to edge out Musselbrugh Athletic.
Talbot's Michael McCann pounced on a poor clearance to drive home from 18 yards after 43 minutes at Rugby Park.
The side newly-promoted to the East of Scotland Super League replied 20 minutes from time following a clinical Chris King finish.
But Brian Young curled a drive in from 15 yards two minutes into added time.
It was the fifth time that Auchinleck, who last claimed victory in 2009, had lifted the trophy at Kilmarnock's stadium in what was virtually a home tie for the Ayrshire side.
King brought Musselburgh level after 70 minutes at Rugby Park
Talbot's Bryan Slaven, the BBC Alba man of the match, said: "I thought we were the best team overall.
"I think there were a bit of nerves in the camp, which surprised me as I thought we would have showed a bit more maturity.
"It was maybe us being overwhelming favourites that affected us a bit and that bit of composure was missing in the early part of the game.
"We are very much a community club and this one was very much for the fans."
The now-defunct Musselburgh Brutonians won the Junior Cup in 1923, but Athletic have yet to taste such success and arrived with their large travelling support as major underdogs.
Talbot, who are third in the West of Scotland Super League Premier Division, dominated the early stages and had already had an effort cleared off the line before taking a deserved lead.
However, the side who beat league champions Irvine Meadow and Junior Cup holders Linlithgow Rose on the way to the final were pegged back after tactical changes brought the Lothian side more into the game after the break.
Young, though, pounced in the penalty box to hand the favourites the advantage in extra-time and Talbot substitute David Gillies went closest to extending their lead with a drive off the outside of a post.
Talbot manager Tommy Sloan said: "It could have went either way at the finish up, but I think we deserved it.
"There was a quality goal there to finish it."