OAKMONT, Pennsylvania — Dustin Johnson didn't understand the rule.
But what he had to do? That was another story. The heartbreak of losing other major championships taught him well.
Johnson kept his cool Sunday while facing a possible penalty for something he claimed he didn't do. He played steady down the stretch before hitting the 6-iron of his life on the final hole — from 192 yards out to 3 feet — to finally win a US Open.
Thankfully for both US Golf Association officials and Johnson, the penalty didn't play a role in the outcome.
"I didn't think that I did anything to cause the ball to move," he said, "but at the end of the day, it didn't affect what happened. So it doesn't bother me at all."
Some lessons learned from a long, steamy day at Oakmont Country Club:
RULES AREN'T ALWAYS RULES: USGA officials debated among themselves after it appeared Johnson's ball moved as he addressed it on the fifth green. But it was clear they were going to penalize Johnson even when he said it wasn't his fault. The ruling drew howls of protests on Twitter from Jordan Spieth, Rory McIlroy and Rickie Fowler. The USGA defended its decision to tell Johnson on the 12th tee he might be penalized, though he didn't know it at the time. Neither did spectators and a national television audience, who were uncertain what his score was or where he stood.
NO MORE MONKEY: Johnson was always considered the most powerful and perhaps most talented player in the game. But he threw away tournaments, including last year's Open when he three-putted from 15 feet to lose to Jordan Spieth. Johnson said afterward that the monkey was off his back, and "it's a huge monkey." Look for Johnson to contend often in the big tournaments, and the odds are good that with the confidence from this Open, he won't be a one-hit wonder.
LOWRY SEASONING: Shane Lowry has won plenty, but winning tournaments and winning Opens are two different things. He started the final round with a four-shot lead, but things quickly got away from him . He ended up shooting a 6-over 76 and tying for second, three shots behind.
"I'm definitely good enough to win one of these," Lowry said. "So I'll get back on the horse in a couple of weeks."
THE CROWN RESTED UNEASY: Jordan Spieth's defense of his title got off to a shaky start. The finish wasn't much better. Eight holes into his opening round, Spieth's near-perfect approach shot landed 15 feet past the flag, spun back and trickled into a bunker.
"You've GOT to be kidding me!" Spieth howled.
On the contrary. Oakmont's rough and its punishing greens got the better of the Texan early and then often. Chambers Bay, where Spieth won last year, was no pushover, either. But he never got on the right side of par here, finishing the tournament at 9 over — his worst finish in a major in which he's made the cut since tying for 44th at the 2013 British Open. He said putting was the biggest issue, which showed on the sixth green when he needed four putts on his way to a front-nine 39.
THE SLIPPER DIDN'T FIT: Andrew Landry arrived at Oakmont under the radar. Make that off the radar.
The 28-year Texan was playing his first major in his first year on the PGA Tour. He was ranked No. 624 in the world.
When Landry shot 66 to become the overnight leader Thursday, then recovered from stumbles in Rounds 2 and 3 with enough grit to play his way into the final pair going off on Sunday, he was in position to pull off one of the great upsets in major championship golf.
Then he hit his opening drive in the right rough, his first approach shot in the left rough and somehow, things went downhill from there .
By the time the final round was over, what began like a story line cribbed from the movie "Caddyshack" — "Cinderella boy about to become the U.S. Open champion!" — turned into an all-too-familiar, crash-and-burn tale from more than one final round of a major championship.
He finished with a 78 and 285 total — nine shots behind winner Dustin Johnson and in a tie for 15th place.
"Walking down 18, I was like, man, I wish I could just take a picture of this because it's like the coolest view," Landry said.