Brendon Todd claimed his first PGA Tour title with a two-shot victory at the HP Byron Nelson Championship in Irving, Texas as Pádraig Harrington dropped down the field after being in overnight contention.
The 28-year-old was playing in the final group of the day with fellow overnight leader Louis Oosthuizen, but, while his South African playing partner struggled to a disappointing 74, Todd kept his calm to fire a bogey-free 66 and finish 14 under.
Mike Weir finished second after a second consecutive 67, with the 2003 Masters champion showing some signs of the form that fired him into the top five in the world.
Harrington started the day just two shots off the overnight leaders but finished tied for 22nd spot with a 74 in a round containing five bogeys and a double plus three birdies, one of which included an outrageous piece of misfortune.
The Dubliner was 63 yards out on the par-four 11th and saw his second shot bounce once before landing directly in the cup but, instead of walking off with an eagle, the three-time Major champion saw the ball bounce out to leave him with a short putt for birdie.
Todd began his round impressively as he holed out of a bunker for birdie on the second and he followed that with further picked up shots at five, nine and 10.
The American looked in trouble at the par-three 13th as his tee shot ended up next to a tree denying him of a natural swing, but the world number 138 played a shot with the back of a club to within seven feet and holed out for par.
Todd left himself in more trouble on the par-five 16th when his third shot failed to make the green, but an excellent chip allowed him to make par and the impressive scrambling continued on the par-three 17th when he rescued another par after missing the green and over-hitting his second shot.
The four on the last proved to be more routine, but Todd acknowledged that saving his par on 17 was a vital moment.
"I asked my caddie walking off the 17th tee where I was," he told Sky Sports. "He thought I was two up so I knew that was a big putt and I jammed it in there."
He added: "It feels amazing, a big monkey off the back. It's been a tough career so far with a lot of ups and downs but I'm excited to be on top right now."
Weir had held the lead early in the day after a blistering start with birdies at one, two four and five, but he gave shots back at six and nine.
Another bogey at 15 was sandwiched by birdies at 13 and 16 as the Canadian came up just short as he looked for a first win since 2007.
Charles Howell was two shots further back after a 67 and looked to be making a charge after pitching in for eagle on 16 and picking up a further shot on the next, but closed with a bogey.
Australian Marc Leishman was also on 10 under after a 68, with James Hahn and Boo Weekley a shot further back.
Dustin Johnson, Graham DeLaet, Gary Woodland and Matt Kuchar were all on eight under, with Kuchar securing a ninth top-10 finish in 13 starts this season.