Clinging to lead, Dustin Johnson told he may lose stroke

— -- OAKMONT, Pa. -- Dustin Johnson won his first major at the U.S. Open on Sunday, despite having a possible one-stroke penalty hanging over his head since the fifth hole.

After a birdie on the 18th hole, Johnson guaranteed himself victory, whether the USGA assessed him a one-stroke penalty or not.

The issue started back on the fifth hole Sunday afternoon. Johnson backed off from a par putt , then summoned a rules official as he apparently had seen his ball move.

Johnson was not assessed a penalty at the time. He made the putt and his score was listed as par.

But United States Golf Association officials told Johnson during the final round that they would review it after the round. If he is deemed to have committed a violation, Johnson will get hit with a penalty stroke.

"We put him on notice,'' said Jeff Hall, the USGA's managing director of competitions. Hall also said during the Fox broadcast that Johnson told him he didn't feel he did anything to cause the ball to move. "We have some concerns,'' Hall said.

Whether Johnson committed a violation is now more complicated under the 2016 edition of the Rules of Golf, which came out in January after a four-year review cycle. Under the old Rule 18-2b (Ball Moving after Address) a player would have automatically been assessed a one-stroke penalty if the ball moved. Under the new Rule 18-2, a player will be penalized if the facts show the player caused the ball to move.

Johnson had a 6-footer for par. He took two practice strokes, then put his putter behind the ball (but didn't ground it) and immediately recoiled as the ball barely moved. It is not necessary for Johnson to have touched the ball for it to be decided that he caused it to move. It could also simply be the very fast green speeds.

After the fifth, Johnson trailed leader Shane Lowry by two strokes, but he made a charge to the top of the leaderboard and led by two after 13. He was clinging to a one-stroke lead after 14 holes.

As others faltered, however, Johnson finished strong to win his first U.S. Open.

Several players, including Rory McIlroy and Jordan Spieth, spoke out on Twitter in defense of Johnson during his round.