After fitting in two rounds of golf into one day, you could forgive Dustin Johnson for feeling exhausted, but last year's U.S. Opener runner-up is flying high.
Johnson - seeking his maiden major title - played 36 consecutive holes at Oakmont on Friday as he earned a share of the one-stroke lead alongside fellow American Andrew Landry.
Among the 78 players not to tee off on Thursday due to wild weather in Pennsylvania, Johnson hit the ground running with a bogey-free 67, which was followed by a second-round 69 to reach four under.
Speaking afterwards, the 31-year-old told reporters: "It was a long day today, but I felt like I played really solid all day for all 36 holes. I drove it really well. Hit a lot of great iron shots. Felt like I rolled the putter really nicely too.
"So very pleased with how it went today."
Asked which was tougher out on course, the physical or mental aspect of completing consecutive rounds, Johnson added: "I think it was a little bit of both. But I'm in pretty good shape, so the physical part's no problem.
"But, definitely mentally you've got to make sure you stay sharp all day, because you can't go to sleep on any shot out here."
The notoriously tricky Oakmont course has played a little easier since the heavy downpour of rain on Thursday.
However, the iconic course is still providing a serious challenge for the world's best.
"It's definitely very difficult. I mean, it's definitely one of the toughest golf courses for sure," he said.
"The greens. They're so hard to putt. No matter how close you are to the hole, it's just, they're tough to putt.
"I hit so many good putts today that I thought were going in, and burned the edge or lip out. But that's just how it goes. These greens are tough."