"Definitely just choked," Mueller said.
Mueller could have a forced a playoff, but he missed a 6-foot putt as Johnson watched from the practice green above No. 18. Some of Johnson's followers cheered loudly in response, which was fairly understandable.
"I wouldn't wish bad things upon anyone," Johnson said, "but it was an unbelievable feeling."
Johnson shot 67-66-68 for a 15-under-par total, earning $21,000 for the victory plus a $750 bonus as the top Utah Section PGA performer.
Occasionally confused with the PGA Tour star of the same name, the 30-year-old Johnson initially pursued a full-time playing career before going settling into a more stable existence as a Davis Park Golf Course assistant. Johnson credited Boyd Summerhays, who has worked with him at Davis this summer, for helping fix some swing issues late Saturday evening and again Sunday morning.
Johnson, a former Cottonwood High School and Southern Utah golfer, acknowledged hitting "some horrendous shots" in the final round. But he delivered immediately after a 37-minute weather delay in the middle of the round. He hooked a wedge shot out of the trees at No. 12, leading to a birdie.
Johnson separated himself from Mueller's other pursuers with a remarkable, 250-yard hybrid shot from the right rough to 15 feet, resulting in the eagle at No. 16.
Mueller, a minitour veteran who played all four rounds of the 2012 U.S. Open, missed some chances to boost his lead in the middle of the back nine. Going into No. 17, he knew his lead was down to one stroke. After a long wait in the fairway, he hit a wedge shot horribly fat and bogeyed, then drove left of the No. 18 fairway. His approach shot clipped a tree and came up short, and he failed to save par.
"I hit a decent putt and it just lipped out," he said, handling himself well in defeat.
Johnson lost a two-stroke lead in the final round in 2009 and has come close in some other Utah Opens, including a tie for third place last August. So he was thrilled to win close to home as Oakridge concluded a seven-year run as tournament host.
Storylines Johnson rallies in Utah Open
R Farmington's Zach Johnson comes from three strokes behind on the last three holes to win by one shot over Arizona pro Jesse Mueller.
• Tournament charity Special Olympics Utah receives a $40,000 contribution.