Catching Martin Kaymer is not the goal for Rory McIlroy and Graeme McDowell. Simply staying around par and seeing how that stacks up on the leaderboard come Sunday night is the only feasible goal right now.

The German has hardly missed a shot in carding two rounds of five under 65 on a PInehurst No 2 course that was softened considerably by Thursday night's torrential downpour, which dumped two thirds of an inch of rain on the parched greens, softening them just enough to allow players to stop their irons when just 48 hours earlier they had been releasing.

Kaymer's two round total of 10 under 130 for a six shot lead over Brendon Todd is the lowest score for the first 36 holes at a U.S. Open, shaving a stroke off the 131 set by McIlroy at Congressional in 2011. Leaderboard

He's just the sixth player in US Open history to reach double digits under par, joining Gil Morgan in 1992, Tiger Woods in 2000, Jim Furyk in 2003, Rick Barnes in 2009, and McIlroy in 2011.

In addition, he joins McIlroy as the only player to be double digits under par through 36 holes at a US Open.

"I think what Martin's doing is more impressive than what I did at Congressional, just because of how difficult the golf course is and there's trouble lying at every corner at any missed green," McIlroy said. "Congressional was a little more benign than this is, a little softer, a little more receptive. So you know what Martin's doing is very impressive."

"I heard he played No. 3 course. Is that true?" joked Kevin Na after a 69 left him tied for third on three under with Brandt Snedeker (69), one behind Todd, who shot 67 to get to four under. 

"It's unbelievable what he's done. Is four or five-under out there? Yes. Ten-under out there? No, I don't think so. I guess it was out there for him. It's amazing, I watched some of the shots he hit and some of the putts he's made and he looks flawless."

No-one expects 10 under to be the winning total at the end of the week but the bad news for Ireland's two cut survivors McIlroy and McDowell is that Kaymer appears to have the mental strength, and the game, to deal with the pressure of holding such an important lead.

As he said after his round: "I probably might think about where I am right now. Yes, I'm thinking about it, but it's all positive. It's a good thing. It doesn't distract me. It's nothing to do with anything, I just enjoy having that chance right now."

McIlroy shot what must go down as his most impressively disciplined rounds in a major to date, a three under 68 after an opening bogey at the par-five 10th to finish the day in the red in joint 10th at one under par.

That it came on Friday the 13th, the day of the week that has caused him the most angst this season, was a nice co-incidence.

And while he's nine strokes behind his Ryder Cup team mate, he's clearly feeling more positive than McDowell, who had a few wobbles on the greens around the turn — he three-putted the 18th from nowhere for a double bogey six and then missed a two footer for par at the first — and did well in the end to limit the damage to a four over 74 that leaves him 12 shots off Kaymer's blistering pace on two over par.

"If I was Martin, hopefully I would be thinking about how to get seven ahead and then how to get eight ahead and then how to get nine ahead," McIlroy said. "It's not something that you, especially on a golf course like this, you can go out trying to protect anything. You've just got to keep the foot to the floor and just keep it going.

"If he's comfortable out here and making birdies, then that's what you should still be thinking of. Ten-under par is an incredible total after 36 holes, and if he can hold on to that 10-under total, he's going to win this tournament.

"As I said, you need that mentality that you're not trying to protect, you're not happy with 6. You want to get to 7, you want to get to 8. That's the sort of mentality you need when you have a big lead like that, because you sort of have to play as if you get too defensive.

"And I learned that at the Masters, the previous Major before Congressional, if you get too defensive, it's detrimental. So he has to just keep hitting to his spots, being aggressive, doing whatever spots he chooses. And if he does that and shoots a couple of 70s over the weekend, I don't think anyone's going to catch that.

Clearly, the field is praying that Kaymer will come back to them, as McDowell explained.

"No one else is going to get to 10-under," said McDowell, who admitted that his short miss on the first left him rattled. "That's a fact. Martin, to me, he's in control of the golf tournament right now, if he can keep it better than five, six-under par, he's got this thing sewn up, I believe, and can only beat himself from here. He's got a lot of work to do, though. The rest of the field has a huge job on their hands.

"All I can do is play my ball. I really have no idea what Martin Kaymer is going to do this weekend. It has little impact on how I'm going to execute my game plan the next two days.

"I just have to try to play a bit more clinically than I did today and make some more putts and a couple of 68's, a couple of 67's, who knows what might happen."

The weather and the USGA have helped players like Kaymer and McIlroy, who hit the ball a long way.

As McDowell explained, a combination of nervousness by the USGA, who watered the course on Wednesday evening, followed by the downpours of Thursday night, has not helped his cause.

"They've taken the course setup Tuesday and Wednesday and backed it off for Thursday and Friday," said the Portrush man after slipping from second to 27th on two over.

"Today was natural circumstances due to the downpours last night, but Thursday morning was artificially brought back. The golf course was slowed down significantly from Wednesday. Now, whether they got a little scared, expected some rainfall that didn't come.

"I would have preferred to see the golf course remain the way it was Tuesday and Wednesday. That would have suited me better. It's given the long guys an opportunity to get short irons in their hand.

"A bit what I talked to earlier in the week, I said that it wouldn't matter if the short iron was in your hands because these greens are so firm. I was wrong. These greens softened up, and short irons were a massive advantage. So the golf course changed, to my detriment. But that's life."

As for his round, McDowell admitted that he lost control around the greens, which is one of his chief weapons this week.

"I hit the ball better than I did yesterday. I just didn't control well. Threw a lot of shots away around the greens. Didn't have the speed at all on the surface. They were a bit slower, and I didn't adapt well to that.

"The three-putt on 18 was killer, after a decent drop shot and missed a short one on one, and just kind of rattled me a little bit. I really grinded hard coming in. And to only be 2-over par at this point in the tournament, I feel like I'm miles back when I see Martin Kaymer at 10-under, but in reality I'm only a few shots out of the top-10.

"And I'm only four or five back off second place. And if that's what we're playing for, then I'm right in the mix. So disappointing day. Not what I had in mind. But this golf course is very difficult, and you don't have to do a lot a round for it to get its teeth into you."

Shane Lowry looked certain to make the cut when he got back to two over for the championship through the turn as he mixed bogeys at the second and sixth with birdies at the fifth, eighth and ninth.

A bogey at the 11th was not a disaster until he double bogeyed the 16th and then bogeyed the last to miss the cut by one stroke on six over par after a second successive 73.

Darren Clarke missed out by just two shots on seven over as he added a 72 to his opening 75. Having started double bogey-bogey, he fought back with birdies at the 14th, second and third but bogeyed the sixth and eighth to miss the cut for the sixth time in 14 US Open appearances.