By Mark Lamport-Stokes

OAKMONT, Pennsylvania (Reuters) - U.S. Open organizers on Monday said they regret "the distraction caused" by their delay in handing champion Dustin Johnson a one-stroke penalty until after Sunday's final round was completed.

The U.S. Golf Association (USGA), however, stood by its decision to penalize Johnson one stroke after the round.

USGA officials had raised the question at the 12th hole of whether leader Johnson would or would not be penalized for making his ball move on the fifth green, despite a ruling on site that he was not at fault.

That decision to put Johnson under notice while informing every other player about his possible penalty, led to a chaotic conclusion at Oakmont Country Club with no initial clarity about the champion's final score.

Johnson later was docked a stroke over the controversial play on the fifth hole, and his official score was amended to 69 for a four-under total of 276, with Americans Jim Furyk and Scott Piercy and Irishman Shane Lowry equal second on one-under.

"Upon reflection, we regret the distraction caused by our decision to wait until the end of the round to decide on the ruling," the USGA said in a statement.

"It is normal for rulings based on video evidence to await the end of a round, when the matter can be discussed with the player before the score card is returned.

"While our focus on getting the ruling correct was appropriate, we created uncertainty about where players stood on the leader board after we informed Dustin on the 12th tee that his actions on the fifth green might lead to a penalty."

The USGA said the delay "created unnecessary ambiguity for Dustin and the other players, as well as spectators on-site, and those watching and listening on television and digital channels".

The handling of the Johnson situation drew outraged responses from several high-profile players via Twitter, including former world number ones Tiger Woods, Rory McIlroy and Jordan Spieth.

Golfing great Jack Nicklaus, speaking during FOX TV coverage of the final round, was among many who criticized the USGA.

"You either have (a penalty) or you don't have one, that's my feeling," the 18-times major champion said. "I think it's very unfair to the player."

The USGA defended the decision to impose the penalty.

"Our officials reviewed the video of Dustin on the fifth green and determined that based on the weight of the evidence, it was more likely than not that Dustin caused his ball to move," the USGA said.

"Dustin's putter contacted the ground at the side of the ball, and almost immediately after, the ball moved.

"We accept that not everyone will agree that Dustin caused his ball to move."

(Editing by Larry Fine)