Pinehurst, United States: Rory McIlroy’s advice to Martin Kaymer about turning his record-low 36-hole score into a US Open title was simple — keep trying to make the lead bigger.

Germany’s Kaymer fired a five-under par 65 for the second day in a row Friday to stand on 10-under 130, breaking the old mark McIlroy set in 2011 by a shot.

Kaymer also matched the low 36-hole start in major history and his six-shot lead over American Brendon Todd after two rounds equalled the record US Open 36-hole leads of Tiger Woods in 2000 at Pebble Beach and McIlroy on his way to winning at Congressional in 2011.

McIlroy, whose 68 Friday left him nine strokes off the pace with 36 holes to play, said his secret that year was to avoid defending his lead by trying to extend it.

“If I was Martin, hopefully I would be thinking about how to get seven ahead and then eight ahead and then nine ahead,” McIlroy said. “You can’t go out trying to protect anything. You’ve just got to keep the foot to the floor.”

McIlroy said he learnt that lesson in 2012 when he squandered a last-day lead to lose the Masters.

“If you get too defensive, it’s detrimental, so he has to just keep hitting to his spots, being aggressive,” McIlroy said. “If he does that and shoots a couple of 70s over the weekend, I don’t think anyone’s going to catch that.”

McIlroy said Kaymer’s feat is more astounding than his own work at Congressional because his own effort came on a rain-softened layout while Kaymer has been overwhelming under more difficult conditions.

“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.”

While some rivals want rain to make the course more receptive, McIlroy wants it to get even drier this weekend.

“I would like for the course to get as firm as possible, because Martin hasn’t really seen it like that,” McIlroy said. “In 36 holes, you never know what can happen. But, Martin is a good front-runner and I can’t see him letting up.”

McIlroy also said organisers could play the course at its full 7,565-yard length to add to the challenge of the turtle-backed greens and sandy, weed-filled run-off areas.

Mickelson ‘not optimistic’

For reigning British Open champion Phil Mickelson, the six-time US Open runner-up who seeks a win to complete a career grand slam, putting woes have him on 143 and admitting “I’m not overly optimistic” about winning now.

“The hole looks like a thimble to me right now. I’m having a hard time finding it,” Mickelson said. “I’m throwing away four or five shots a round. It’s very frustrating.”

Mickelson, however, warned that no lead is safe when double bogeys lurk on every hole as poor shots are well punished.

“You never know in a US Open,” he said. “We’ve had a lot of crazy things happen. There are a lot of guys waiting right there if he slips up.”

Behind Kaymer, only 12 players are under par and only three — Todd and fellow Americans Kevin Na and Brandt Snedeker — are within eight strokes.

“Stick to your game and just keep playing good US Open golf,” Todd said of his strategy. “If you can play each nine one-under par, you’re probably doing really good.

“Avoiding the bogeys I think is number one. And then if you can make birdies with the short clubs, that’s number two.

“And that’s what’s going to catch him.”