Brittany Lang landed her first major title at the U.S. Women's Open after Sweden's Anna Nordqvist was given a two-stroke penalty but only informed belatedly.
There, Johnson was hit with a one-shot penalty for an infraction on the fifth green when the ball moved as he addressed it.
But he was only informed that he could be penalized on the 12th tee and appeared unsettled, dropping a shot on the 14th before steadying himself to take the title.
Nordqvist was punished after TV replays indicated she had grounded her club when addressing the ball in a bunker at CordeValle Golf Club in California.
The incident -- a breach because it is deemed to constitute testing the conditions of the sand -- happened on the second hole of a three-hole playoff against Lang, with the scores level.
United States Golf Association (USGA) officials told Nordqvist of the breach -- which she did not dispute -- and penalty after she had played her third shot to the final playoff hole.
The 29-year-old said at a news conference: "I just wish they would have told me a little earlier. It might not have changed anything, but I just wish it was a little bit earlier.
"I couldn't really believe that it happened. It wasn't my intention to ground the club. It's been a long day, a long week. So I probably misjudged it a little bit and touched a little bit of sand, and that's a penalty."
Lang, 30, was informed before she had played her third shot, and Nordqvist said: "It certainly changed her game plan.
"I don't know if it would have changed the outcome, but it certainly would have changed my aggressiveness into the 18th pin."
Lang shot par on the final hole as Nordqvist three-putted to end up losing by three strokes.
The Texan said: "They should tell you as soon as they know. I really don't think today was that big a deal. Anna happened to [have] hit her third shot.
"They have to check these things, and it's not that easy. I said sorry to Anna. I know she is probably super mad."
Lang's maiden major victory earned her $810,000 and is only her second win on the LPGA Tour
-- she won the LPGA Classic in 2012, also in a playoff.
"Yeah, it's pretty special. I've always dreamed of winning the U.S. Open... I just feel like I have extremely underachieved as a golfer," Lang told reporters.
"I feel like I'm so capable of doing so much more than I've done. And this is just a little start to boost me."