Goalkeeper Jordan Brown was the Rob Roy hero with two penalty shootout saves as the Kirkintilloch side claimed their first cup in over 40 years.
After Sunday's exselgroup Sectional League Cup final with Shettleston at Cambuslang had ended goalless Brown saved the first two Shettleston kicks.
In contrast Lee Gallacher, Kevin Green, Gary McMenamin and Willie Sawyers all netted as Rob Roy captured the trophy for the first time since 1974.
Watched by a crowd of 646, the match produced a nervy opening period.
The first chance fell to Shettleston in the fifth minute but Lewis Kinnaird skied the ball over from distance. Then a Greg McDonald shot skimmed the Rabs crossbar.
As the half progressed Rabs pushed forward for the opener but found the well organised Shettleston defence hard to break down.
Rabs had their best chance when Craig Buchanan headed wide before Kevin Watt's goalbound shot was blocked.
Rob Roy won a number of corners but found Shettleston goalkeeper Dean Trainor in commanding form.
Both sides had chances to snatch a half-time lead. Watt scissor-kicked a Gavin Mackie cross over the bar before, at the other end, Peter Weatherson ran through on goal but was denied by the offside flag.
Mackie then chipped across the Shettleston penalty area but there were no takers and the sides went in all square at the break.
Rob Roy began the second half brightly and Watt and Chris Duff had shots blocked.
Rabs kept up the pressure but their final ball into the penalty box let them down with the tall Shettleston defence mopping up any danger.
In a Shettleston break upfield only a last gasp tackle by Buchanan prevented Weatherson running in on goal.
On the hour mark Shettleston substitute Welsh fired just over in front of goal and then danger man Weatherson's shot trundled past Brown's post.
There was a scare for Rabs in 67 minutes when Brown spilled a Weatherson free-kick and the ball fell to Welsh who missed the target from point-blank range.
Rob Roy were reduced to 10 men in the 77th minute when Shaun Fraser was sent off for a wild tackle on Rikki McIntosh.
Welsh then had a in the 70th minute for Shettleston but his shot was blocked for a corner.
In the dying minutes Gallacher fired over for Rob Rob Roy as they pressed fort a winner.
Then a tackle by McMenamin on Welsh prevented Shettleston taking a last-minute lead.
The action still wasn't finished as, in stoppage time, Weatherson - a constant danger to the Rabs defence - headed over the bar, taking the game to a penalty shoot out.
Brown saved from Halsman and McIntosh while Gallacher, Green and McMenamin all netted for Rabs, although after scoring his kick McMenamin was shown a red card for an offensive gesture to the Shettleston supporters.
Shettleston scored their next two kicks but when Sawyers netted Rabs' fourth kick the cup was bound for Kirkintilloch. Man of the match, not surprisingly, was keeper Brown.