DeChambeau started preparing for a playoff after his birdie putt at 18 trickled in for a seven-under-par 64 that matched the low round of the day and brought him to 20 under on the week.
But it still wasn't enough as Xander Schauffele sealed the deal with a birdie of his own at the last to crush DeChambeau's hopes of a second major title.
"You know, shot 20-under par in a major championship. Proud of myself for the way I handled adversity," DeChambeau told reporters.
"Definitely disappointing, but one that gives me a lot of momentum for the rest of the majors. I said today it was closing time, but it will be closing time hopefully, hopefully over the next couple majors."
DeChambeau, who led the field in driving distance, was near automatic while stringing together a bogey-free final round and managed to deliver nearly every shot he needed as the stakes got higher deeper into the round.
He was also the recipient of some good fortune at the par-four 16th where his tee shot was headed for thick rough before it bounced off a tree and into the fairway.
DeChambeau went on to make a birdie after his approach shot from 219 yards out settled three feet from the cup, which moved him one shot back of the lead and put a spring in his step.
"I looked at (my caddie Gregory Bodine), and I go, okay, this is what it takes to win major championships. You got to have breaks like that happen," said DeChambeau. "I fully took advantage of that second shot, put it in there close, hit a great shot."
DeChambeau had a great week on the greens and showcased a brilliant short game but still felt like he was not firing on all cylinders and said he only had his "B" game this week.
If there is another gear to DeChambeau's game, he could certainly do some damage at next month's US Open where he is sure to once again be a fan favourite.
"I gave it my all. I put as much effort as I possibly could into it and I knew that my B game would be enough. It's just clearly somebody played incredibly well," said DeChambeau.
"Xander's well deserving of a major championship and, yeah, emptying the tank, certainly love to do that and give the fans everything I can."
