The Dubliner (19) went into the final two rounds tied for second, four shots behind Roganstown star Seán Keeling (17) at pristine Dun Laoghaire.
But 49 years after Joey Bryan lost to Martin O’Brien in the Close final at Cork and 54 years after David Sheahan denied Mark Bloom at Grange, the Maynooth University talent showed a maturity beyond his years to beat Dun Laoghaire’s Richard Sykes (32) at the second extra hole.
“It’s class,” said Abom, who had his sister Anna, a girls international, on his bag. “I mean, long day. I don’t really know what to say. I’m just overridden with emotion.
“It just feels great. Finally, a lot of release just to make that putt at the end just feels really good.”
Keeling’s title chances all but evaporated with a quintuple-bogey nine at his sixth hole in a third-round 79 before going on to finish fifth on one-under.
But Abom carded a one-under 71 in the morning round to head former hockey international Sykes by one stroke on six-under.
Sykes played magnificently to forge a two-shot lead early on the back nine but leading Abom by a shot playing the last, he bogeyed the 18th to shoot 71 and Abom birdied the 17th to take the lead.
The Edmondstown man needed a par to win but took three to get down from a yard short of the green, carding a 72 to tie with Sykes on six-under.
Abom lipped out from 20 feet for birdie and victory in the driveable 13th. But after Sykes shaved the hole from 25 feet on their return to the 18th, the eventual champion rifled a 146-yard nine-iron to three feet and rolled in the putt for victory.
“Definitely the best in my career,” Abom said of his glory shot. “Yeah, you can’t really top that, right at the pin, definitely number one in the circumstances.”
Royal Dublin’s Hugh Foley was third on three-under after a closing 69 with Ballybofey and Stranorlar’s Ryan Griffin fourth after a closing 66.
On the PGA Tour, Rory McIlroy endured a week to forget in the FedEx St Jude Championship as he closed with a four-over 74 to finish tied 68th in the 70-man field on nine-over par.
The world No 3, who struggled on the greens and off the tee, made a triple-bogey six at the 14th as well as three bogeys and a solitary birdie at the first.
Shane Lowry also failed to fire at the weekend as a one-over 71 left him tied for 51st on one-under.
On the DP World Tour, David Ravetto claimed his maiden victory with a four-stroke win in the D+D REAL Czech Masters.
Trailing Jesper Svensson by a shot overnight, the Frenchman closed with a sensational eight-under 64 to win on 24-under at PGA National Oaks Prague as the Swede shot 69.
“It’s indescribable; I’m just super happy,” Ravetto said.
On the Challenge Tour, Mornington’s Daniel Mulligan (19) clinched a career-best finish when he tied for 27th with Naas’ Conor O’Rourke in the Vierumaki Finnish Challenge. Mulligan made an eagle and two birdies in a two-under 70 to share 27th on 12-under par as O’Rourke also shot two-under.
Sweden’s Christofer Blomstrand closed with a seven-under 65 to secure his first Challenge Tour title by a shot from compatriot Mikael Lindberg and France’s Alexander Levy on 20-under as first-round leader Mark Power shot 72 to finish 42nd on nine-under.
Meanwhile, Leona Maguire closed with a 74 to finish 61st on nine-over in the ISPS Handa Women’s Scottish Open at Dundonald Links,
American Lauren Coughlin made it two wins in three starts after she rattled in three birdies in her last five holes en route to a three-under 69 for a four-shot win over Germany’s Olympic silver medallist Esther Henseleit on 15-under.