SOUTHAMPTON, N.Y. – Dustin Johnson would appear to be the envy of golfers everywhere – long drives, precise iron shots, a deft touch around the greens and a putting stroke to die for.

But when you're halfway home to a second U.S. Open championship in three years, as Johnson is after his 3-under-par 67 on Friday at Shinnecock Hills Golf Club left him with a 4-stroke lead, you look past the physical gifts and see that he has the mental makeup to succeed in this incredibly challenging championship.

Through two days in changing conditions, including some unexpected rain Friday morning that proved to be more than an annoyance over seven holes in mid-round, Johnson stayed patient, calm and unflappable. Maybe more important, he didn't try anything crazy by forcing the issue after a bad shot.

"A couple of times (Thursday), I was a little bit out of position, but I'm just trying to get it back in play and then give myself an easy look at par," said Johnson, who carded just one bogey Friday. "I feel like if I can get a look at par and not make any doubles, I'm going to make a couple birdies. But it's limiting the mistakes, especially the big numbers. I never want to make doubles.

"I know I'm playing well, so as long as I can do that, then I'm going to shoot a pretty good score."

Johnson's 36-hole total of 4-under 136 was exactly the same when he captured the 2016 Open at Oakmont. A number of players tried to cut into the deficit in the afternoon amid a barely detectable breeze that made scoring a little easier, and Justin Rose, Charley Hoffman and Ian Poulter got into red numbers only to fall back.

Poulter had the cruelest reversal. One shot off Johnson's lead on his 17th hole, he knocked his second shot into a bunker but caught the sand shot flush and flew his ball well over the green. After a chunked chip and a battle with the fescue, he walked off with triple bogey.

With a bogey at his last hole, Poulter fell to a five-way tie for fourth at 141 with Rose, Henrik Stenson, Tommy Fleetwood and defending champion Brooks Koepka, who matched Fleetwood's 66 for the best round of the championship thus far. Rose bogeyed each of his last two holes.

Hoffman bogeyed the 18th for a 69 that tied him for second with Scott Piercy at 140. Piercy, who made the field as an alternate and was one of four first-round leaders, shot a 71 and will play in the last group with Johnson.

Johnson looked serene on the course. He didn't really react to any of his four birdies except for a 45-foot downhill putt at the par-3 seventh that just barely found the bottom of the cup.

"I knew about halfway there it was on a really good line if it would just get to the hole," he said. "I guess it dropped right in the front door."

That helped give him a commanding lead at the halfway point even though he did get the less favorable side of the draw – windy conditions with faster greens Thursday afternoon, unexpected rain and cooler conditions Friday morning.

So he's fine as he enters the weekend with the lead, something he prefers over trying to chase down the leaders. He said he would sleep just fine.

"Usually I don't have trouble sleeping," he said. "But yeah, there's still a lot of golf left … 36 holes left no matter what position I'm in. Going into (Saturday), I'm going to stick with my game plan, stick to trying to play the holes how I have the first couple days and see what happens."