Harmon was speaking to Off The Ball ahead of this week's Ryder Cup
Butch Harmon believes Dustin Johnson's recent form is reminiscent of Tiger Woods at his peak.
Speaking to Off The Ball ahead of this week's Ryder Cup in Hazeltine, Harmon explained what changes he has seen in the US Open champion that has inspired such high praise.
"Well I think it started with the birth of his son," he began. "I think Dustin becoming a father has had a big influence on him, a big responsibility that he's never had before.
"I see a lot more of a mature Dustin Johnson than I've seen. For years I've been trying to get him to fade the ball off the tee when he needed to hit the fairway, and he's bought into that beautifully. Now he hits a fade most of the time, and he's turned himself into a fantastic driver.
"Not only does he hit one of the longest drives, but he's getting 60-65% of his fairways. Then his wedge was the weakest part of his game, and we talked at the end of last year that he had to improve his proximity to the hole from 150 yards in. Quite frankly, he plays about every hole from inside about 150 yards.
"He has worked his tail off at that. He's taken the weakest part of his game and made it a strength."
Johnson reeled in Shane Lowry in the final round at Oakmont, and even had the mental strength to play through a potential stroke penalty, a move which was widely praised by fellow players. The USGA only revealed after his round that he had incurred the penalty.
"You know winning a major championship... I said it all along when he wins one, the floodgates are going to open and he's going to win a lot of them.
"Not that he wasn't confident before, but he plays with a different confidence now. He knows who he is, and he knows his golf game. He's worked harder.
"I told him after he won a couple of weeks ago, he's starting to remind me of Tiger Woods in the old days. He hits it as far as anyone, he puts it in the fairway better. His short game is better, and he's starting to be that guy that, when he's on, he's almost impossible to beat."