And so to the final tee for Dustin Johnson. Shane Lowry is hoping he makes a mistake. The tee shot starts left but fades perfectly and this will land in the middle of the fairway. Wonderful shot. 

As Johnson walks off the tee he gets a pat on the back from Lee Westwood. People are hoping he gets over the line here to render any issues the rule makers may throw up meaningless.

-4 Dustin Johnson (US) (17) 

-1 Shane Lowry (Ire) (16), Scott Piercy (US) (18), Jim Furyk (US) (18), Branden Grace (SA) (17)

E Sergio Garcia (Spa) (18)

Lee Westwood is in the cup on 17. Just the 10 over for today. My oh my, that's a nightmare right there.

Dustin Johnson for birdie on 17. 

This will break from right to left. He eyeballs it, it's the type of scrutiny a Lion gives its prey, looks good... a shade wide.

So it's a par putt of some two feet, never in doubt.

Now then, he's four under and three clear. Even if he gets docked a shot he will win the US Open as things stand.

Image source, Getty Images

Iain Carter
BBC golf correspondent at Oakmont Country Club

"There are traits there showing on the popular bearded man from Ireland that suggest he is a beaten man. It should not be that way."

Image source, Getty Images

Scott Piercy is two under and has a long putt for par on 18. Like all of them here it has a lot of break in it, the pace looks good, the line isn't and he will drop at least one.

Shane Lowry, I feel for him, I think we all do. He's not the subject of the rule confusion - that's Dustin Johnson if you are just tuning in - but Lowry has felt the impact for sure and he pushes his putt past the hole on 16. That's him back to one under.

Dustin Johnson is in a greenside bunker after a tee shot on 17 but hold your horses, it's a par four so he has shots to play with to limit damage.

He's just walking up to the bunker. He'll be cautious here. Jason Day got greedy on this hole and flew the ball from one sand trap to another.

Image source, Getty Images

Branden Grace has given himself some hope as he walks onto 18. A very good read and beautifully weighted putt on 17 moved him to one under. His tee shot at the last goes way right though.

Shane Lowry on 16 has 50ft for birdie and he leaves it short of pace, it'll break right and leave a mess of a putt for par. Lowry looks a little in shock. Slightly dazed by the confusion which has engulfed this famous piece of sporting real estate.

Iain Carter
BBC golf correspondent at Oakmont Country Club

"Everyone who loves golf knows it has its nuisances. But my fear here is that the rest of the sporting world will take one look at golf and just leave it and that's what gets my goat. This could have been dealt with in a much better way."

There's a hint of a Rocky film about this. You know the one where Rocky wins over a hostile Russain crowd.

Dustin Johnson is getting a lot of love. "DJ, DJ, DJ," chant the crowd. They think he's been wronged (or could be wronged) and they are willing him home.

Jay Townsend
Former American professional golfer on BBC Radio 5 live sports extra

“That putt was a great save as it was not a great chip shot on to the green. That showed a lot of heart.”

Image source, EPA

What a putt from Dustin Johnson. His knees would have been clattering together viciously and he holds still in his stance until it drops. Then comes the fist pump. Big.

There's something ironic here in that Dustin Johnson is asking a rules official for guidance now just off the back of the 16th green because his foot is on a sprinkler when he takes his stance for this crucial shot.

DJ decides he will not take a drop because he's concerned with how the ball would come to rest. He elects for height with this chip, whipping the club face under the ball. It settles eight feet from the flag.

As the daylight dwindles...I don't fancy him to make this.

It's Father's Day, so here's some guidance for all the dads out there from Will Gray of the Golf Channel.

Get the little ones down the driving range in the morning gents.

Chris Wood is currently tied for 23rd on seven over.

While Shane Lowry flounders and Dustin Johnson's score remains under question, Scott Piercy's mark of two under with one to play looks as lovely as a roast dinner.

He can't quite make birdie on 17 as a putt slips away but one more birdie at the last will perhaps win this for him?

Remember, 18 has given up one birdie all day.

Image source, Getty Images

Iain Carter
BBC golf correspondent at Oakmont Country Club

"I don't think the USGA will apologise.

"They will argue that they have done nothing wrong and followed the rules. They have informed the player, they are reviewing the footage and they will chat to the player before he signs his card. As soon as he signs the card, it can't be changed.

"I think the protocol is wrong. In every other sport the referee makes a decision on the spot. If he gets it right or wrong, the decision is made, and they move on."