Paul Dunne produced a fantastic closing 61 to hold off a late charge from Rory McIlroy and win his first European Tour title at the British Masters supported by Sky Sports.
The Irishman turned in 30 to lead by three at Close House Golf Club and looked to be cruising to victory before World Number Six McIlroy birdied five of his last seven holes in a 63 to get to 17 under.
That gave Dunne a one-shot lead with two to play but a birdie on the 17th eased the pressure and the 24 year old chipped in on the last for a 20 under par total and a three-shot victory.
Swede Robert Karlsson rolled back the years to finish third on 16 under, two shots ahead of countryman David Lingmerth, local favourite Graeme Storm and German Florian Fritsch.
Dunne had a stellar amateur career, playing in the Walker Cup and leading the 2015 Open Championship after 54 holes but this is his first professional win in his 51st European Tour event after losing out in a play-off to Edoardo Molinari at the Trophée Hassan II in April.
"It's kind of a sense of relief to prove it to myself that I can get it done," he said. "I think I've improved a lot mentally over the last year in these kind of situations.
"I feel like I've got a bit tougher mentally and I get excited to go out and look at the leaderboard, rather than trying to look at position.
"I went out and really tried to win the tournament rather than have someone hand it to me. That was the focus. Once I was in front, just keep pushing, make no bogeys and see how many birdies I can make. Absolutely thrilled.
"Obviously the money is great. It means I don't have to worry about getting a job where I have to sit behind a desk. But after all this, you know, I really love playing golf, and I've been grateful."
Dunne started in brilliant fashion, chipping in for a birdie on the first, and after another gain at the fourth he produced a beautiful tee-shot to birdie the par three fifth.
A fantastic second shot into the par five sixth brought an eagle and Dunne got an incredible stroke of luck on the 11th as his approach hit a sprinkler head and bounced to within four feet for another gain.
He took advantage of the par five 13th for the fourth time this week and despite McIlroy applying the pressure, he held his nerve as he nearly drove the short penultimate hole and book-ended the lowest round of his European Tour career with another chip-in on the par three last.
McIlroy made the most of the par five sixth, holed a long putt on the seventh and got a nice bounce off the bank for a third birdie in a row on the eighth but when he missed good opportunities on the ninth and tenth and bogeyed the 11th, his race looked to be run.
Nice approaches into the 12th and 14th sandwiched a gain on the par five 13th for another hat-trick and while he missed a good chance on the next, a good approach to the 16th and chip on the 17th piled the pressure on Dunne.
"It was good," said McIlroy. "It was just nice to have a chance to win a golf tournament. I think that was the big thing. The more chances I have like that, I seem to play better. Mentally I'm just a little more engaged and switched on.
"I started okay today. I started a little more slowly than yesterday but I was three under through nine. Saw that Paul got off to a great start and I set myself a target on the back nine. I said, if I could shoot four under on the back nine, finish 17 under, I'll have a chance.
"I did everything that I wanted to do, it just wasn't good enough in the end today.
"Incredible, to shoot 61 to win his first Tour event, it's incredibly impressive. I'm happy for him as well. He works hard on his game. Every time I'm out practising or on the putting green, the chipping green, he's always there and he's always working hard. So it's very well deserved."
Karlsson, 48, bogeyed the fourth but gains on the fifth, ninth, 11th, 13th and 17th gave him a 66 and his best result of the season.
Fritsch - 155th in the Race to Dubai Rankings presented by Rolex - boosted his chances of keeping his card with a closing 66 while Lingmerth signed for a 66 and Storm carded a 67.
Ireland's Shane Lowry also recorded a 67 to finish at 13 under, a shot ahead of Dane Lucas Bjerregaard, England's Tyrrell Hatton and Scot Richie Ramsay.
