John Catlin overturned a four-stroke deficit at Galgorm Castle Golf Club, firing a sublime final round 64 to win his second European Tour title of the season at the Irish Open.
The American started the day four strokes behind 54-hole leader Aaron Rai but quickly moved up the leaderboard as he made the turn in three-under par.
He pulled clear on the 16th hole and then signed for a ten-under par total.
Rai birdied the 17th to move to nine-under, needing a birdie to force a play-off, but an errant second shot found trouble and a dropped shot handed Catlin his second victory in four weeks - after winning at Andalucia Masters.
"It's pretty hard to describe. So many years of hard work have gone into this moment. It was my goal to win again at the start of this week, to have accomplished it is something truly, truly special," said Catlin.
"(Winning at Valderrama) was massive. You never know if you're going to win or not, to get that monkey off my back at Valderrama really freed me up today to know I could do it. Be able to look myself in the mirror and tell myself that I've been here before and I can do it again."
South Africa's Dean Burmester, who was two strokes back ahead of the final round, had a day to forget as he carded a 75 to finish T22 on 1-under par.
Justin Harding ended as the best-placed South African as he finished T11 at three-under par.
Leading scores from the final round of the European Tour's Irish Open in Ballymena on Sunday (GBR/IRL unless stated, par 70):
270 - John Catlin (USA) 67-70-69-64
272 - Aaron Rai (ENG) 65-70-67-70
273 - Jazz Janewattananond (THA) 68-70-66-69, Maverick Antcliff (AUS) 70-65-68-70
274 - Joakim Lagergren (SWE) 70-66-71-67, Oscar Lengden (SWE) 67-71-66-70
275 - Fabrizio Zanotti (PAR) 70-72-70-63, Lucas Herbert (AUS) 71-67-67-70, Jordan Smith 65-71-70-69
276 - Adrian Meronk (POL) 71-69-70-66
277 - Justin Harding (RSA) 68-69-69-71, Joost Luiten (NED) 71-70-69-67, Scott Hend (AUS) 68-69-70-70
- Compiled by Sport24 staff