Warrenpoint's Colm Campbell holed two clutch par putts on the 17th and 18th to force a playoff with Malone's Matthew McClean before capturing his second Flogas Irish Amateur Open title with a bogey at the first extra hole at The Island.
The 35-year-old golf rep, who was champion at Royal Dublin in 2016 but is now a part-time golfer, had low expectations starting the week.
But after following rounds of 73 and 75 with a three-under 69 on Saturday to go into the final round just a shot behind Castle's Robert Moran on one-over-par, he used his vast experience to add a second Irish Strokeplay crown to wins in the East of Ireland and Ulster Strokeplay.
"It's a little bit different than 2016," said Campbell, who made a 10 footer at the 17th and a 12 footer for another par at the 18th for a level par 72 to tie with McClean on one-over 289.
"Obviously, I was playing a full-time schedule back then, so my expectations were a little bit lower. But I knew I was playing well enough and as I said last night, I wasn't here to make up the numbers."
Campbell found himself in front when overnight leader Moran double-bogeyed the third and shot 75 to finish third on three-over.
But McClean followed a bogey at the fourth with birdies at the fifth, sixth and ninth to tie for the lead with Campbell and Moran on one-over through nine holes.
He then eagled the 10th and birdied the 13th to go three clear on two-under.
But Campbell did not panic, and after drawing level when McClean ran up a double-bogey seven at the 15th and then bogeyed the 17th, he followed that clutch par putt at the 17th with another at the last to shoot 72 to McClean's 70.
On their return to the 18th in sudden-death, McClean had to take a penalty drop after driving into the right rough, then bunkered his third and failed with a 15 footer for bogey as Campbell came up 50 yards short left in two but pitched to 25 feet to set up a winning two-putt bogey.
"There might be a few pints in Warrenpoint tonight, but I have to go to work tomorrow morning and then play a Barton Shield match tomorrow night," joked Campbell. "But I'm delighted to get over the line, so there's still a little bit of golf left in there yet. I am a happy man."
On the DP World Tour, Royal Dublin's Niall Kearney closed with a two-over 73 to tie for 15th on six-under, seven shots behind England's Sam Horsfield in the Soudal Open in Belgium.
Just three shots off the lead overnight, Kearney bogeyed the 10th, 11th and 15th before making his lone birdie of the day at the 17th as Horsfield shot 68 to capture his third DP World Tour title by two strokes from Germany's Yannick Paul (69) and New Zealander Ryan Fox (71) on 13-under-par.