Billy Horschel ended the hopes of Victor Perez at the WGC-Dell Technologies Match Play with a 3&2 victory over the Frenchman in the semi-finals.
Horschel will now play Scottie Scheffler, who defeated Matt Kuchar 1up, in an all-American final at Austin Country Club, with Perez taking on Kuchar in the third-place play-off
Perez, 28, was in fine form in Texas on Saturday and dropped only one shot all day during impressive defeats of Bob MacIntyre and Sergio Garcia.
But the 31st seed struggled in the blustery conditions on Sunday morning, making six bogeys to hand Horschel victory, despite the 32nd seed playing what Paul McGinley on commentary described as "as bad a shot as you will ever see by a professional golfer".
Horschel's nightmare moment came at the par-five sixth when he duffed his third shot, allowing Perez to go 1up, although he hit back immediately by levelling it up at the next hole with a par.
Perez missed from 10 feet for his par at the 10th and then found water after pulling his tee shot miles left at the par-three 11th as Horschel went 2up.
The Frenchman, who lives in Dundee, escaped with a half at the 12th despite finding the water again with his second shot, but another short missed par putt at the 14th allowed the American to go 3up.
Perez gave himself a chance with a brilliant approach shot to four inches as he took the 15th hole, but a poor second which came up short of the green at the par-five 16th allowed Horschel to seal the win with a birdie.
"It was a challenge today," said Horschel. "It wasn't one of those days you go out and make a lot of birdies. Sort of had to grind it out and understand pars were good scores. I did a good job of that. Victor made a couple of bogeys.
"I didn't play anything special. I just played solid golf and let Victor make a few mistakes."
On his effort on the sixth, he added: "It was literally the bad club. Should've hit seven-iron and I was trying to hit a chippy, chippy six and I just hit it fat. I've done it before and I'll probably do it again in my career.
"So it was one of those things you just move on and try to hit a better shot next time."
Scheffler, who like Perez is making his debut in the tournament, and Kuchar had a hard-fought battle in the second semi-final.
Kuchar, 42, went behind after making a mess of the second, flirting with rocks down the left off the tee and then finding the penalty area at the back of the green with his second.
Scheffler, however, made his first bogey in 46 holes when he missed a short putt at the fourth to allow 52nd seed Kuchar to level.
The 24-year-old was back in front when he holed an 11-foot putt for birdie at the ninth and he then sank an 18-footer at the 11th to double his advantage.
But the 30th seed found water at both the 12th and 13th to enable Kuchar to level again and they halved the next three holes before Scheffler drained what proved to be a match-winning putt from 10 feet for a birdie at the 17th, with Kuchar then missing from 15 feet for a birdie as the 18th was halved.
Scheffler said: "I felt really good about how I was playing all day. My stroke felt good. My swing felt very good and I was comfortable. I think I was almost too comfortable. Kind of lost focus on 12 and 13. 12, bad shot. Can't do that. Had to keep the pressure on him. Thirteen I really hit a good shot. I don't know how it came up short.
"I felt good about my game and I knew if I kept executing and hitting good shots I would have a chance to win."