Tiger Woods was relieved to keep double-bogeys off his card after battling to a four-over-par 74 in the US Open second round on Friday.
The world number one, hunting his 13th major title, piled up six bogeys and two birdies to end a gruelling day at Oakmont Country Club five strokes behind the pacesetting Angel Cabrera of Argentina.
"It was playing really hard out there, " twice champion Woods told reporters after posting a five-over total of 145 on a firm, fast-running layout.
"The greens got really quick and it was hard to try and place the ball under the hole.
"It was a lot more difficult than yesterday and the wind was changing directions ever so slightly, so you had to be aware of that.
"I felt like today's round could have gotten away a little bit but I didn't make any doubles. Unfortunately I had a three-putt on 15 but other than that I hung in there really well today."
Putting on Oakmont's infamous sloping greens often became a lottery, Woods said.
"I probably had three putts today where I felt I could be aggressive and I made two of them," he added. "It's just so hard out there and the pins were a little more difficult than they were yesterday."
"They weren't flat, they were just on some ridges and all of a sudden you have a good putt that goes five, six feet by."
US Open champion at Pebble Beach in 2000 and at Bethpage Black in 2002, Woods knows the last two rounds will provide a severe mental test.
"I've won this championship before and you have to be patient," the 31-year-old American said.
"Good shots are not going to be totally rewarded and bad shots are going to be penalised. You know that and that's the way it should be.
"If they don't water the golf course, it's going to be a lot more difficult tomorrow. It's going to be a test for all us."
Woods, who has won two of the last three majors, is looking forward to a "fun challenge" over the weekend.
"This is the US Open, it's going to be tough and you've got to grind away," he said. "That's the fun part of it, it's so different than any other tournament we play in."