American Brittany Lang won her first major title at the US Women's Open in a play-off with Anna Nordqvist after the Swede was given a two-stroke penalty.
USGA officials told Lang of the penalty before her third to the last green but Nordqvist found out after her approach.
"I wish the USGA would have told me a bit earlier," said Nordqvist, 29.
"They approached me after I already hit my third shot into 18, then kind of ran up to Brittany to tell her that I got penalised.
"I don't know if it would have changed the outcome, but it certainly would have changed my aggressiveness into the 18th pin."
The penalty was incurred with the scores level, and was only picked up after television replays indicated the Solheim Cup player had moved sand as she addressed the ball.
Rules state a player 'grounding a club' in a bunker will incur a two-shot penalty because they are deemed to have been testing the conditions.
Lang made par on the final hole with Nordqvist three-putting the last green to make a bogey and lose by three strokes.
It is the second USGA-run major to be dominated by a ruling in three weeks after Dustin Johnson played the majority of his final round of the US Open at Oakmont not knowing if he would be penalised because his ball moved as he addressed it on the fifth green.
Nordqvist had forced a play-off with a five-under final round of 67, with Lang's one-under-par 71 leaving both women on six-under for the tournament.
Lang, who was addressed as Bethany by USGA president Diana Murphy at the trophy presentation, said: "I'm thankful they told me before my wedge shot so I could take a little bit more club.
"They should tell you as soon as they know. I really don't think today was that big of a deal. Anna happened to hit her third shot. They have to go look and check these things. It's not that easy.
"I just said sorry to Anna [at the end]. I know she is probably super mad."
Nordqvist agreed she should have been penalised, saying: "It wasn't on purpose. It's just one of those things. I have to deal with the consequences."
Murphy later apologised for getting Lang's name wrong, saying: "I have expressed my regret to Brittany personally and explained that in the heat of the moment, I became nervous and made these mistakes."
Overnight leader and world number one Lydia Ko, seeking her third major as a teenager, shot a three-over 75 to finish in a tie for third on four-under.
Ko made a double bogey and two bogeys in the middle of her round as she went from leading after eight holes to two adrift of Lang and Nordqvist.
England's Jodi Ewart Shadoff shot a two-under 70 to finish in a tie for eighth place.