Some believed the USGA was displaying deference to one of golf's most popular figures, though, by making a very narrow interpretation of the rule (14-5) governing that situation, one that says, "A player must not make a stroke at his ball while it is moving".
Andrew Johnston, who was paired with Mickelson, was stunned by the incident and broke into laughter, prompting the American to also grin as the pair walked off the green.
"John Daly's reputation took a hit after what he did at Pinehurst in '99 and I fear it will be the same for Phil", said former U.S. Golf Association executive director David Fay. "It was just a moment of madness, but nothing disrespectful", said Johnson.
It was a childish display from a five-time major victor celebrating his 48th birthday.
Mickelson was slapped with a two-stroke penalty and finished with 10 strokes on the whole, six over par.
He missed that putt as well and then tapped in for a 10 with the penalty he had to take, putting him at 10-over for the day and in a position where he's going to have some explaining to do. Like anybody, good people make mistakes. At that time, I just didn't feel like going back and forth, hitting the same shot over.
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Mickelson insisted he was not frustrated by the more hard hole locations in the third round.
He then two-putted for 10, with the penalty. And as it released and went through, I thought, 'Wow, that is seriously quick'. "He made a stroke at a moving ball, which is explicitly covered under 14-5". The result: Brooks Koepka shot an un U.S. Open-like 16-under par to win, and 31 golfers broke par. You always want to use them in your favour.
"I think you've got to because it was outrageous what they did to the course".
BBC golf correspondent Iain Carter said: "It was a deliberate breach of the rules".
Johnston and Mickelson shared a laugh about it going off the 13th green, but Johnston wasn't quite sure what he was laughing about. He had those four consecutive bogeys before a par at the 12th.
Just imagine what a joke it would be if every player, both in the amateur and professional games, set out from now on with Mickelson's mentality of trying to save the odd shot here or there if a ball was heading towards either a bunker or a hazard.
It certainly was one of the most surreal moments of all the 118 U.S. Opens contested.