Northern Ireland's Rory McIlroy endured "bad breaks" in a "frustrating" second round at the Masters where an 18th-hole putt saw him make the cut by one shot.
The two-time major champion started the day one under, but dropped four shots on the back nine to shoot 77 and finish four over par, 11 shots off the lead.
"It was very frustrating," said the 24-year-old. "I just really couldn't get anything to go my way.
"Eleven shots back is going to be nearly impossible to make up."
McIlroy, the US Open champion in 2011 and USPGA Championship winner in 2012, had no idea his testing putt on the 18th had to drop if he was to stay in the tournament.
He admitted it "was a bit of a sigh of relief" to still be involved, but rued his luck during a round in which an approach shot into the 13th green bounced off a sprinkler and into bushes, forcing him to drop a shot.
Watson has only ever won one of eight tournaments he has led at the halfway stage, but if McIlroy is to win, he will need to close the biggest deficit in Masters history - an eight stroke come back by Jack Burke in 1956 is the current best.
In pursuit of American Watson, Britain's best-placed players going into the weekend are Welshman Jamie Donaldson and Scotland's Stephen Gallacher, who both sit on one under par.
Gallacher, a Masters debutant, birdied the par-five 15th as he ended the day on the same mark as he started.
The 39-year-old hit 12 of 14 fairways from the tee, but admitted he was "glad to still be in the red numbers" after a round which included four bogeys.
"You've got to keep your temperament," said Gallacher. "Your acceptance levels here have got to be through the roof, you've just got to hit it, accept it and get on with it.
"It's a very strategic course. I think everyone at home knows how to play it but it's just a case of trying to do it."
Donaldson described his standing at six shots behind Watson as "a good position", but acknowledged he has "to try to hit more fairways" over the weekend after finding just 14 of 28 so far.
On day two of the tournament, Augusta National's four par five holes played the easiest statistically, with 143 of the day's 290 birdies and seven eagles arriving on the quartet.
Lee Westwood was unable to capitalise on their generosity for the second day running and finished one under par for the day and level for the tournament.
"I didn't play the par fives well enough again," said 40-year-old Westwood who is still searching for a first major title. "Over two days, I've made eight fives and that's where you make your scores. You need birdies over the weekend on them.
"There's good scores if you play well and disasters if you start hitting a few wild shots. I'm comfortable out there and can see a way around it."
US Open champion Justin Rose and fellow Englishman Ian Poulter both carded scores of 70 on day two to move to two over for the tournament.
"That was one of the best rounds I have had at Augusta in terms of ball striking, but I finish disappointed because I left shots on the course," said Poulter.
"I three-putted at 10 and at 14. I know I am playing well, my scores are not reflecting that but they are coming and I need to stay patient."
Elsewhere, Northern Ireland's Graeme McDowell conceded "Augusta is still a work in progress" for him after missing the cut along with England's Luke Donald.