Adam Scott, Jason Day and Aaron Baddeley failed to capitalise on a faltering Martin Kaymer in round three at the US Open.

World No.1 Adam Scott has admitted being too cautious after failing to take advantage as runaway US Open leader Martin Kaymer finally showed vulnerability on a brutally difficult Pinehurst No.2 course.

After posting the lowest total in US Open history through 36 holes to lead by six shots at 10-under, German star Kaymer’s two-over-par 72 third round was still good enough to lead by five from Americans Rickie Fowler (67) and Erik Compton (67), a double heart transplant recipient.

Scott battled to a 73 and fellow Australian Jason Day a 72 to be three-over – a distant 10 shots behind Kaymer – in a tie for 16th and needing a miracle.

Kaymer could become only the seventh wire-to-wire US Open winner, joining Tiger Woods, Rory McIlroy, Walter Hagen, Ben Hogan, Tony Jacklin and James Barnes.

Not since Mike Brady squandered a five-shot lead in 1919 has a US Open 54-hole leader had such a margin and failed to win the title.

“I’m looking forward to see how I react to certain situations,” Kaymer said. “Anything can happen. I can lead by seven or eight shots after nine holes. I can be down to all square. So it will be an exciting round.

“It’ll be interesting how I handle it.”

World No.2 Henrik Stenson (70), who could take Scott’s No.1 status with a win if Scott finishes outside the top four, and Dustin Johnson (70) share fourth at two-under.

Aaron Baddeley, the only other Australian to make the halfway cut from 11 starters, shot 73 to be four-over and tied 23rd.

“I might have played a bit too cautious,” Scott lamented.

“Today was a bit of a letdown.

“Every round, I’ve got under par after the first half a dozen holes and only one day I’ve managed to keep it going so that’s a little disappointing.”

In extremely hot and dry conditions and playing a very tough course set-up that allowed only two sub-par rounds on Saturday, Scott started strongly with some impressive par-saving efforts over the opening four holes.

The Queenslander than pumped a drive down the par-five fifth and hit a beautiful six iron to two metres with his second.

But his eagle putt lipped out forcing him to settle for a birdie and rather than ride the momentum forward he stumbled as the par-three holes bared their teeth.

Scott bogeyed three of the four par threes, blunting his charge.

Despite being so far back, particularly for a US Open where birdies are like hens teeth, Scott vowed to attack on the final day.

“I’m going to try to get it in the fairways and then I can try and find some shots to hit a little closer to the hole,” he said.

“I feel like I’ve putted beautifully this week but it’s hard to just walk in 40 footers, so I’m going to have to find a way to get it inside 20 feet tomorrow.

“And at least if I could post a number in red figures, you never know.

“I’m going to have to have a pretty special round to even think about those dreams.”

AAP be/rj/nh/rw