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Dustin Johnson plucks his driver out of the bag on the 372 yard par-four 16. It looks a little bit aggressive. It does skip though, but sticks on the green just about at the back.

JB Holmes meanwhile is scrapping around for a par at 18th as his third shot from the hay at the back of the green rolls all the way through and back into a bunker.

In the end it takes a gutsy ten-footer to preserve his one-under status.

Jay Townsend
Former American professional golfer on BBC Radio 5 live

Jason Day has never held a 54-hole lead in a major. He is in the clubhouse tied for the lead on four under.

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Branden Grace's arms are swinging a little less freely.

But the South African gives his birdie putt enough of a poke to stuff it away on the 15th.

We have a three-way tie at the top of the leaderboard with Dustin Johnson and Jason Day also residing on four under.

Branden Grace has tickled a lovely tee-shot to within five feet at the par-three 15th.

Jordan Spieth has suffered a bad break on 14 with his approach going walkabout after he had placed it carefully close to the pin.

The young American rescues his par with a bold putter that rattles right in,

JB Holmes is too strong for his own good on the par-five 18th, banging a fairway wood though the back of the green with his second shot.

It was right on line as well. Unlucky.

Shane Lowry after a level-par 70: "The greens are not 100% but the golf course is still a good golf course. When I got here on Monday and played 36 holes practise. I thought it was a bit funky but the more I play it the more I like it. Most of the shots are there in front of you."

Image source, Reuters

The Icelandic ash cloud of 2010. The Hemel Hempstead depot cloud of 2005. Might the Chambers Bay fug of 2015 be one of the all-time great clouds?

Promising form and colour from the new comer.

Iain Carter
BBC golf correspondent on Radio 5 live sport

What a brave performance. The story of the day. Jason Day with a brilliant birdie-birdie finish to get to four under par and a share of the lead. We didn't even think he would be playing today.

Pin a medal on that man's chest.

Jason Day, who has been swallowing and blinking like a new-born pup for most of the day as he keeps his vertigo under control, is now joint leader.

His birdie on the last bring the 6,000-strong grandstand to their feet and moves him up alongside Dustin Johnson at the top of the leaderboard.

Johnson is only heading south at the moment as well.

Image source, Reuters

Jason Day with an absolute peach of a shot on 18, finding the sweet spot in the centre of the club and a helpful slope. He will have a great chance to pull up alongside leader Dustin Johnson with a birdie chance from five foot to come,

Branden Grace makes par on 14 with a long worming putt. He stays at three under.

JB Holmes gives a shot back on 17 to move back to one under though.

Branden Grace has dropped a shot on 13th. It is all going off.

So let's take a moment and have a little mini run-down on what's going on:

-4: D Johnson

-3: Day, Grace, Speith.

-2: Holmes

-1: Oosthuizen, Smith Lowry, Luiten

And they are the only men under par for the tournament,

Image source, AP

Ireland's Shane Lowry is done and dusted with a quietly effective round keeping him right in the hunt.

Level par for the day and one under overall. That is a platform for a final-day push if ever I saw one.

Jay Townsend
Former American professional golfer on BBC Radio 5 live

It's a great course for a major championship because you don't know what's going to happen next. You might not like the course but you cannot deny the excitement.

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JB Holmes, welcome to the equation.

The American, who like Jason Day drove the 370-yard green and watched his ball trickle into the sand, splashes out from the greenside bunker at 16, running the ball up the hill and then watching as it rolls back down and right onto the bullseye for an eagle two.

Sensational shot and the frat-boy shouters in the crowd enjoyed that. Holmes is two under and hot on the heels of the leaders.

Chris Jones
BBC Radio 5 live commentator at Chambers Bay

This is turning into a famously gutsy effort by Jason Day.

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It is getting mighty cramped in here.

Dustin Johnson comes pinging back to the pack with a double bogey on the 13th.

A massive roar over on 17 where Jason Day's ball as trickled down the pipe for a birdie. He is now back to three under and within a shot of Johnson and Branden Grace.

Jay Townsend
Former American professional golfer on BBC Radio 5 live

The pressure is getting greater. Nothing is ever straightforward. That's why it is compelling watching.

Dustin Johnson is tapping around the 13th green to little effect.

He now faces a tricky seven or eight footer downhill for a bogey.

Playing partner Branden Grace misses his own par putt as well.

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Jason Day is soldiering on in fine style. He steps back from his tee shot at the par-three 17th apparently suffering from some of the effects of his vertigo.

When he does hit it, it is a beat, dotting down for a 12-foot birdie putt. The Australian has to take a knee as he retrieves his tee out of the ground.

Jordan Spieth is off 12 with a par by the way,

Leader Dustin Johnson is in a bit of bother on 13th. His third from the bunker flops tamely into the middle of the green and he has some considerable lumps and bumps to negotiate if he is to get off here with a par.