Rules officials took a look and agreed.
"After a full review, it was determined that Thompson breached Rule 20-7c (Playing From Wrong Place), and received a two-stroke penalty".
Thompson was leading by two when she was informed by a rules official on the 12th hole that she was to incur a four-shot penalty for her third round.
Last night's debacle further brought to the surface the dissatisfaction both players and fans have with golf's governing bodies, with social media erupting with fury over the incident that cost Thompson the first major of the season.
Thompson handled it all with class.
"[The fans] got me through the whole round", Thompson said after the playoff.
Other contenders include gallery favorite and three-time victor Phil Mickelson, red-hot Spaniard Jon Rahm and Japan's Hideki Matsuyama who is trying to become the first Japanese man to win a major.
Dustin Johnson has been the talk of golf over the last two months, and that was sure to at least help McIlroy manage the expectations. "I am really appreciative of everything right now", Ryu added". "It's unfortunate what happened". I didn't realize I did that.
Rickie Fowler was 3 over after four holes and didn't make up ground until it was too late.
"I had to regroup myself, my caddie helped me out tremendously, we have a great relationship".
"No, we haven't spoke about it", Willett said. "You're not going to have to hit ideal golf shots, but you're going to have to leave it where you can get up and down or where you can 2 -putt from wherever that may be". But it's all to the fans.
"They really got me through the whole round", she said.
"I thought I was well behind (Lexi)". "It's a hard thing to do, and it made me sick, to be honest with you". "Even some of my losses in the majors, I try to take the positive out of it and learn from it and do better the next time".
Q. Mike Tirico said what you did on 13 and there on after defines what an athlete is. I think it's been an ongoing problem.
"I'm proud of my entire round", he said twice. Just the way I played coming in.
"He's a guy that you know that when you're paired up, he's been there and you don't feel like you have that major championship winning edge", Spieth said. "I fought strong and that's all I could do". I was like, "perfect, there you go".
"I just wanted to say a quick thank you to not only everyone in the room here, through their well wishes and prayers, from peers to sponsors to, all the sponsors to fans; the amount of text messages and emails that I got and my agent got, I mean, it meant a lot", Day said.
Thompson isn't the first player to have been affected by golf's incredulous rules. Wasn't expecting that on whatever hole that was. "I didn't intentionally do that".
Thompson did not complain about the call and did not lash out at rules officials. She fought extremely hard and played unbelievable golf.