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Patrick Reed has practically got a theodolite and set square out to measure up a mammoth eagle putt on the par five. Drain this and he is leading solo.

It is a risky one though, heading downhill. He gives it a tickle and even that was a bit heavy. He has six feet to negotiate back up the hill.

Dustin Johnson's momentum is checked with a bogey four on the ninth.

He is still at the top of the tree though on six under. His lead over Ryder Cup compadres Jordan Spieth and Patrick Reed is down to one shot though as rounds the turn.

He is solid and secure off the 10th tee

By the way, Dustin Johnson has the whole clan over to watch this charge at the top of the leaderboard.

Wife Paulina Gretzky, son Tatum and father-in-law Wayne are all at Chambers Bay.

If Tatum doesn't live out the plot of Happy Gimore with Dustin Johnson as his dad and Wayne Gretzky's daughter as his mum, there is no hope..

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Rory McIlroy with a long look at a long-range birdie putt on the par-five eighth.

He might as well have been trying to read Ancient Greek as that green. The ball stayed stubbornly out left, refusing to break as he thought it might.

A frustrating day continues.

Cheers Peter.

Rory McIlroy's indifferent form at least takes him out of the thorny "best-placed Brit" issue.

That honour is currently held by Marc Warren of Scotland on one under through seven, with Paul Casey, one over and done for his day, his nearest competition.

Dustin Johnson on the par-three ninth. And he's in the sand. One yard from perfection.

Back on the eighth and Rory McIlroy is chipping his third from short of the green. It hops and skips and comes to rest 15 feet from the pin. If ever he needed a birdie.

Perhaps Mike Henson can bring him more luck than I. Let's find out...

That's three birdies in five holes for Dustin Johnson on some of the hardest holes on the course. Sergio Garcia, by contrast, has shipped three in the last four.

Scotland's Marc Warren is fighting hard. A birdie on the 15th has got him back to one under for the tournament.

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Big swing at the top of the leaderboard.

Dustin Johnson gets all aggressive with his eagle putt on the eighth but trundles in for birdie from five feet to get to seven under.

Patrick Reed pays the ultimate penalty for missing the fairway on the seventh. His third from the back of the green gets diverted by on a huge slope and the par putt stays up. He drops back to five under, level with Jordan Spieth.

Sergio Garcia's decent start is in danger of unravelling. A bogey on the seventh and he's just raced a birdie putt on the eighth six feet past and his putting woes continue. The Spaniard suddenly out to +2.

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Patrick Reed has no cut pressures at the moment but he is playing to the seventh green out of the claggy rough to the left of the fairway. He can't hold the green and has a tricky up and down for par.

Colin Montgomerie gives himself a chance of picking up a shot on the par-three 17th with a decent tee shot into the guts of the green.

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Rory McIlroy is in danger of missing the cut. His birdie putt from the back of the seventh green leaves him a dozen feet for par. But he's not making that and the world number one is right on the cut line at +3.

Bubba Watson eyes up the bunker shot on the second and flies it way up into the air. It lands softly but he's got work to do for par.

On the seventh, Martin Kaymer's defence could be ending today. He doesn't borrow enough on a lengthy birdie putt and misses the 15-foot par putt that follows. He's back to +4.

Dustin Johnson finds the par-five eighth green in two. A 25-footer for eagle.

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Bubba Watson with a wild swish from the rough on the second and he is heading into a greenside bunker. He is +3 and on the cut mark.

Rory McIlroy smashed his drive down the seventh into Dustin Johnson country but he cannot match the American's accuracy with a wedge in his hand. His ball skips over the mound that Dustin's rolled back down towards the hole. Instead of a three-foot putt, Rors is facing a 40-foot birdie attempt.

Niall: Dreams of Monty and Speith being paired together in the final round. Thirty years/stone between them, neck and neck going down the home stretch.

Back to the seventh for Dustin Johnson's birdie attempt. I did him a disservice. His approach finished three feet from the pin. A much easier putt and Dustin duly obliges to join Patrick Reed as US Open leader on six under par.

Patrick Reed crouches down behind his birdie putt on the sixth. It's similar to the one Rory McIlroy just missed, maybe a touch longer and he misses to the right, just like Rory.

Sergio Garcia, never the greatest putter in the world, is a touch short with a birdie putt on seven but he is level for the round and tournament and hanging in there.

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Lee Westwood on Twitter: , externalPlayed great today. Shame about 18. I know I made triple but it's a stupid par 4 and a great par 5. Sun and wind on this golf course all day. Chambers Bay will be brutal this afternoon. Great viewing.

Dustin Johnson takes full advantage of his monster drive on the seventh. His short iron stops abruptly and then dribbles back towards the hole leaving a six-foot birdie putt.

Phil Mickelson misses a birdie opportunity on the par-five first but is in for par to stay +2.

Henrik Stenson's putting radar is also slightly off but he stops the rot of successive bogeys with a par on the 16th to stay three under.

Rory McIlroy's birdie putt on the sixth races a couple of feet past but he has more nerve than Monty and holes out. Back down the fairway, Patrick Reed hits his approach pin high but he's 30 feet left of the pin.

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Monty for birdie on 15 from 20 feet and that's meandering right, a testy couple of feet for par. And he's tugged that left. A three-putt bogey and a third successive bogey sees the Scot back to one over par.