Overlooked for so much of the week, Simpson emerged on a fog-filled Sunday at The Olympic Club with four birdies around the turn and a tough chip out of a hole to the right of the 18th green that he converted into par for a 2-under 68.
He finished at 1-over 281, and it was enough to outlast former U.S. Open champions Jim Furyk and Graeme McDowell.
Furyk bogeyed two of his last three holes. McDowell had a 25-foot birdie on the 18th to force a playoff, but it never had a chance.
"Oh, wow," Simpson said, watching from the locker room.
Olympic is known as the "graveyard of champions" because proven major winners who were poised to win the U.S. Open have always lost to the underdog. One of those was Arnold Palmer in 1966, when he lost a seven-shot lead on the back nine.
Perhaps it was only fitting that the 25-year-old Simpson went to Wake Forest on an Arnold Palmer scholarship.
"Arnold has been so good to me," Simpson said. "Just the other day, I read that story and thought about it. He's meant so much to me and Wake Forest. Hopefully, I can get a little back for him and make him smile."
No one was beaming like Simpson, who followed a breakthrough year on the PGA Tour with his first major.
No one was more disgusted than Furyk, in control of the U.S. Open for so much of the final round until he snap-hooked his tee shot on the par-5 16th hole to fall out of the lead for the first time all day, and was unable to get it back. Needing a birdie on the final hole, he hit into the bunker. He crouched and clamped his teeth onto the shaft of his wedge. Furyk made bogey on the final hole and closed with a 74, a final round without a single birdie.
McDowell, who made four bogeys on the front nine, at least gave himself a chance with a 20-foot birdie putt on the 17th and a shot into the 18th that had him sprinting up the hill to see what kind of chance he had. The putt stayed left of the hole the entire way, and he had to settle for a 73.
McDowell shared second place with Michael Thompson, who closed with a 67 and waited two hours to see if it would be good enough.
Tiger Woods, starting five shots behind, played the first six holes in 6-over par and was never a factor. He shot 73.