Enough quips have been made about Dustin Johnson’s IQ to give serious give serious thought to debunking the theory that golf is a game played on the six-inch course between the ears.

US columnist Rick Reilly once quipped that Johnson was so talented he was capable of anything, before cruelly adding that he’s also “so dense, light bends around him.”

The American added a 69 to his opening, bogey-free 67 to share the lead on four under with PGA Tour rookie Andrew Landry at a still soft but rapidly drying Oakmont, where power and accuracy off the tee has always been key to victory.

It was key for Angel Cabrera in 2007 as he unsheathed his driver on the back nine on Sunday and blasted three drives over 350 yards en route to victory. 

And it will be important again this week, not only for Johnson, but for Shane Lowry, whose prowess with a lob wedge is matched only by his skill with the biggest club in the bag.

A two under 68 left the pride of Co Offaly in holiday form at the Pittsburgh venue early on Friday morning where he played the last seven holes of his weather-delayed opening round in two under par thanks to some brave driving and superb, gutsy putting.

After solid pars at the 12th and 13th, he hit a five iron off the tee and sand wedge to eight feet at the 14th and holed the putt for birdie to get into the red at a US Open.

He then saved par from close to 20 feet at the 15th when he missed the fairway in the first cut and his approach ran into a difficult spot against the collar of rough around the green.

He fist pumped after that putt went down and then made a crucial two-putt par at the 16th after leaving his 35-foot birdie putt at least five feet short.

At the 17th, he went for the green with his driver rather than laying up, the ran his pitch and run up to 'gimme' range from heavy and birdied there to go two under before closing with a solid, two-putt birdie at the 18th, once again cleaning up solidly from four feet.

“Any time you shoot 68 around this golf course is a good day,” said Lowry, who had 27 putts and drove the ball well. “I’m really happy the way I went out this morning. I holed some nice putts, some key putts coming in.

Lowry has felt positive about the challenge of Oakmont from the start and believes a good attitude is key despite the difficulty of the course or the irritation of the weather delays.

He also believes that it’s important to be aggressive off the tee, especially with the course softened up by rain and the proof of the pudding is in his score.

“I was more aggressive today,” he said. “You have to hit driver. When you hit a good tee shot you can be more aggressive into greens and it will stop.”

Rory McIlroy was too conservative early on and then too wayward when he did take his driver as he slipped to a 77. And it was a similar tale for world No 1 Jason Day, who also played for position too much early on and then soared to an opening 76 when he tried to be aggressive and was still five over with three holes of his second round to complete this morning.

Rather than going on the defensive, Lowry’s attitude to the tough rough, the speedy greens and the weather delays has been to take it all as an enjoyable challenge.

“I find the guys that are moaning about it are guys that are going to be going home early,” he said. “You just have to get on with it. That's Mother Nature.”

His positive attitude extended to his thoughts on why he has failed to build on some fast starts in events this year in the Waste Management Phoenix Open, the Honda Classic, the Masters and The Players.

“I’ve been shooting  some good scores on difficult golf courses. I’ve been playing well. I just haven’t been putting four rounds together. I don’t know why.

“Obviously, last year at the US Open has helped me a lot. I contended there and felt like I played really well coming down the stretch on Sunday. 

“This year at the Masters, good first round again. I’ve shot a lot of good scores on Thursday this year. I just need to put four of them together. 

“As soon as I put four of them together, I think it will be close enough.”

Putting is Lowry’s Achilles’ heel — he’s 84th for strokes gained putting on the PGA Tour this year.

And that’s why he was so animated after his round.

“The putt on 15 was massive,” he said. “And 16, just to keep myself under par. You miss one of those and all of a sudden you are struggling to shoot level. But standing on 17 one under, you think if I can sneak a birdie here and pick up one more, that’s a great score.”

“To shoot 68 around there is pretty good. I knew coming out this morning that I would definitely need to par it in because although the wind is supposed to get up and the course will dry out, if you hit it in the fairways there are chances out there, but if you miss it is quite tough. To play those last six holes in two under was really nice.”

Returning to his putting, he said: “Even that little one on the last, that makes lunch taste much better. You miss that one and you are a bit disappointed with the day, even shooting one under.”