Tiger Woods was hit with a two-stroke penalty in a dramatic start to the third day of the Masters at Augusta National on Saturday.
The world number one had reached the halfway stage three shots behind leader Australian Jason Day and firmly in contention for a 15th major title and fifth green jacket.
But a review of the drop he took at the 15th hole on Friday after his ball had hit the pin and spun back into a water hazard, showed that he had inadvertedly broken the rules and he was sanctioned with a two-stroke penalty.
That turned what could have been a birdie four into a triple-bogey eight and left him mired back in the chasing pack, trailing by five shots with the second half of the tournament about to get underway.
Day, seeking to become the first Australian to win the Masters, shot a day's best 68 on Friday to take the lead with 1992 champion Fred Couples and another Australian, Marc Leishman, tied for second place on five under.
Argentina's 2009 Masters winner Angel Cabrera, US veteran Jim Furyk and Brandt Snedeker shared fourth place a further stroke back and there were 27 players at or under par within six strokes of the lead.
Day, who tied for second at Augusta National two years ago on his debut, said that he needed to stay in the moment and not let the pressure of leading the Masters get in the way.
"Obviously there's a lot of pressure on my shoulders, being from Australia and no Australian has ever won the event," he said.
"They have been very, very close, but I've just got to try to get that out of my mind and just plug away."
On Saturday, Day will partner 53-year-old Couples, a huge favorite with US golf fans and a regular contender at the Masters, placing in the top 15 for the last three years.
"Just an amazing guy," Day said of the American. "A guy, I'm not too sure how old he is, he's in his 50s, but the guy can still move the ball a long, long way, can still hit great shots.
"It's just great to see him up on the leaderboard. He's such a great guy, and you know, I'm hoping that he plays well."
Couples said he simply did not know whether he would stay the course mentally and physically over the weekend's 36 holes.
"Am I good enough to play four good rounds in a row on a course like this? It didn't happen last year," he said.
"I was four over pretty fast on Saturday, which was a real bummer. And then on Sunday, you know, I played well enough to finish in a good spot.
"But you know, when I get to be a certain age and I don't start driving it where on the last hole I have a four- or five-iron in there, it's going to be impossible for me to play well here, physically impossible."
A total of 61 players made it through to the weekend and by far the most surprising was 14-year-old Chinese schoolboy Guan Tianlang, the youngest player by far in Masters history.
Guan was controversially hit with a one-stroke penalty for slow play when he was on the 17th hole on Friday and he was left hanging for several hours uncertain whether he would become the first player from China to make the cut.
Eventually, he squeezed into the weekend as he was within 10 strokes of the lead and will partner Denmark's Thorbjorn Olesen.