"To be honest, I was not good through 27 holes and the fact I had no chance and shot 19-under after that, it's pretty ridiculous", said Rahm.
"That combined and not guessing over too many things, certainty helps on the golf course".
Meanwhile, Reed made it hard for anyone to question his moxie. He had to two-putt from 35 feet for eighth victory of his PGA Tour career. He punched out, the ball scooting off the back of the green, but he got up and down for par, knocking in a testy 11-footer to stay within one of the lead. He made par on No. 13 and No. 14 before using his run of birdies to win the tournament.
And that's when Reed always seems to get better.
DeChambeau led by three early in the round and still was tied on the back nine when he made three bogeys over the last five holes - one of his pars was a three-putt on the par-5 15th - and had to settle for a 71.
But a three-putt bogey at the par-three 17th proved too much to overcome as he settled for a six-under par 65 and a 17-under total of 267. Reed seized on the moment. Blocked by the edges of trees left of the 16th fairway, he hooked a gap wedge that rode the ridge of the 16th green and fed down the slope to 3 feet.
The satisfying victory capped a week in which Reed again found himself criticized - this time by compatriot Brooks Koepka - for an incident at the Hero World Challenge in December when video showed him moving sand behind his ball in a waste area.
And so it was that Reed had not one but two grenades tossed his way this week in the wake of Sandy-gate in the Bahamas, the "cheating" scandal that continues to dog him.
"Those guys are in your group, you know you have to step up and play the best golf you can because you know how high calibre the guys are". Better yet, the Spanish player is in the mix in Mexico. "You understand the integrity that goes on". I mean, come on.
Reed said Saturday he was just trying to concentrate on his game.
All he did Sunday was win. To which, Reed gave a replay that will have more than a few rolling their eyes.
"I think I played some really good golf the last four days, and I think I can hold my head high", said Van Rooyen after his round on Sunday.
He finished at 18-under 266 and moved to No. 8 in the world.
But whatever anyone's take on the rights and wrongs of Reed's behaviour on the course, it appears to be water off a duck's back. He has taken his brunt of criticism for his pace of play, feeling as though he has become a target.
"It was a lot of fun", DeChambeau said.
"I think a lot of us like to talk sometimes of how unlucky we get and today I was fortunate", said world number three Rahm. My team knows that when I'm playing in tournaments, I'm kind of in my zone doing my thing.
Jon Rahm finished third, two shots behind on 15-under following a 67. He had to scramble for double bogey, and his lead was down to one, and then gone when Thomas began the back nine with consecutive birdies.