Jordan Spieth acknowledged that Augusta had provided an extremely tough mental test on Friday after his Masters lead was cut to just one stroke.
Despite birdieing two of the first three holes to briefly open up a five-shot advantage, defending champion Spieth registered his first over-par score in 10 rounds at Augusta as a mixture of gusting winds and lightning-fast greens made for the stiffest of challenges.
Rory McIlroy was one of only four players to break par in round two, a 71 lifting the Northern Irishman to three under and a place in Saturday's final group with Spieth.
After saving par at the last to complete a 74 and reach the halfway stage at four under, Spieth said: "I think I can use the back nine today as a learning experience. It was very tough to stay cool. I mean, it's a lot easier said than done.
"It was a dream start obviously. But boy, that golf course changed very much throughout the day.
"We were trying to adjust with ever-gusting and changing winds. It just was a really difficult day to score."
Augusta's greens appeared to get faster and firmer as the day progressed, but Spieth is confident action will be taken to ensure a fair test is offered over the weekend.
"I don't think there's a chance they will get out of control," said the world number two.
"I think that the tournament committee understands the conditions for tomorrow. They are able to kind of have it down to a science.
"I think courses where you don't have that kind of system and you don't go there every single year so you can develop that, there's more of a chance for that [greens becoming too fast] to happen. I don't think there's a chance it will happen here.
"They need water on them tonight and I'm sure there will be water on them tonight. I think it will still be fair, but it will be very tough."