So what a day of golf it has been. Dustin Johnson and Andrew Landry lead the way, both on four under.

Landry only had to play one shot today, while Johnson had to not only finish his first round, but then also play his whole second round.

Our live text commentary will be running from about 13:30 BST on Saturday and it promises to be another dramatic day with a host of big names battling to stay in contention.

So bye for now and we will see you again later on. Thanks.

Here's how it stands at the end of day two:

-4: Dustin Johnson (F), Andrew Landry 

-3: Lee Westwood

-2: Scott Piercy (F), Shane Lowry, Sergio Garcia (F)

-1: Daniel Summerhays (F), Andy Sullivan (F), Scottie Scheffler (a), Bubba Watson, Kevin Streelman, Danny Lee, Jim Furyk (17*)

England's Andy Sullivan, who is on one under overall, tells Sky Sports: “I was aggressive and it paid off. I hit the driver really well, which opened up the greens and I had lots of birdie chances.

"This morning, in Oakmont standards, the greens were really slow but they got quicker this afternoon.

"I recently re-employed my psychologist as mentally I was struggling, and I feel majors like this patience is the key and I needed help with this. Hopefully the pins will stay where they are and I can continue to be aggressive."

Image source, EPA

And there goes the hooter. Frustration for a few, who will have to finish their second rounds tomorrow.

Jim Furyk and Graeme McDowell both have one hole left, Justin Rose has two holes left to play and the trio of Jason Day, Adam Scott and Louis Oosthuizen all have three more to play early tomorrow.

What an end from Sergio Garcia. His last shot of the day, a 40-foot putt to save par on his last hole, and he nails it. A puff of the cheeks, the club held aloft. He ends on two under overall, and is definitely in contention for his first major triumph.

Dustin Johnson taps in to par his last. His one under round of 69 is enough to see him end the day with a share of the lead, along with fellow American Andrew Landry on four under overall.

Landry still has to play his second round, and that joy comes tomorrow.

Image source, Getty Images

Iain Carter
BBC golf correspondent at Oakmont Country Club

"Cars have put their headlights on and it's getting dusky. Players are rushing to get holes finished. I'm pretty sure we'll be hearing the klaxon soon."

Image source, Phil Casey

Great athleticism, skill and balance from Sergio Garcia, who not only manages to connect with the ball in the deepest of deep roughs, but also sends it in the intended direction on the ninth. He also manages to avoid falling over, when lesser mortals would have embarrassed themselves so good work all round.

Justin Rose is in the deep rough on the 16th, has his arms crossed, deep sighs and is looking thoroughly fed up.

Rose, a US Open winner three years ago, is on four over for the round, six over overall and is another who may well not be seeing much action for the rest of this weekend.

Image source, Getty Images

Mickelson is now on seven over, 11 strokes adrift of Dustin Johnson and Andrew Landry.

Forget any talk of winning the one major to elude him, he is in grave danger of missing the cut.

He needs to be in the top 60 (plus ties) when everyone has completed two rounds or it is going to be a very quiet weekend for the American.

Mickelson is in tied 94th at the moment, but, remember, half the field have not started their second round yet.

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Jason Day can at least have a chuckle. He is two under in round two, but inches away from that becoming three under, with his shot kissing the left edge of the hole, but with the ball saying on the green.

How much will Day's opening round, earlier today, of six over, cost him?

The world number one is tied 45th, but that is a lot better than it looked like being earlier on.

Six feet to save par. And it is no problem for Dustin Johnson. The weight is perfect, the direction is perfect, the outcome - in the middle of the hole - is perfect. One hole to go for the joint leader.

Sergio Garcia also saves par at the eighth, and he is on two under overall, two strokes behind Johnson and Andrew Landry.

Back to the eighth, where co-leader Dustin Johnson, after a short tee shot, throws a delicate chip to within six feet away of the hole as he aims to save par on the par three.

The score of the second round has come from American Daniel Summerhays, whose 65 has left him on one under for the tournament, and in tied seventh.

"30 on the back nine, I can't describe it. In the US Open. I'm absolutely thrilled," says an ecstatic Summerhays in an interview on Sky Sports.

"My speed was way better in the second round. My putts were rolling in at just the right speed.

"I was waiting for four days to find out if I had qualified after losing the play-off and then I waited to find out my tee time. Then I found out I had two tee times and had to play 36 holes in 24 hours but playing like that, I'll take it."

Image source, AP

It is getting dark, very dark. We may be ending this a bit earlier than hoped. This is going to be so frustrating for those who won't finish round two today. But, at the moment, we continue.

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Dustin Johnson collects another par, two more holes for him today. Well, that is what is scheduled.

Adam Scott on the fourth has an eagle opportunity, but leaves it eight feet away. He then misses the birdie attempt, shooting to the left of the hole. He throws the club up in the air in frustration.

Jason Day has had a miserable day. Although a birdie, his second in three holes, slightly cheers him up.

Another golf superstar has a good moment, on a disappointing day. Phil Mickelson's long birdie on 14 to bring him back to six over. That is the first birdie, on his 14th hole of the round.

England's Lee Slattery, who is level par after a second round score of 68, has just been talking to Sky Sports.

He says: “It feels very good. Daniel (Summerhays) obviously played better than me but we just kind of fed off each other all day.

"I think the short game is key round here this week. Adapting to the change in the greens was important as they got faster this afternoon. It doesn’t matter if it’s up hill, downhill, side hill. Every putt is quick.

"I’m so tired at the moment that I don’t really know what’s going on. It’s been a really tough day around a very tough golf course. It’s been mentally demanding.”

Image source, Gett

Image source, Getty Images

Sergio Garcia gets a bit of fortune on the seventh. The ball hits the ridge to the right of the green, and then rolls and rolls down the green, leaving him well placed. He is running after the ball, as he wants to finish his round today.

Three more holes for Garcia, but the light is fading fast. Finish it tonight, and he will get more time in bed tomorrow morning. If he does not get to finish his second round tonight then that alarm clock will be going off earlier than he would like on Saturday.

Iain Carter
BBC golf correspondent at Oakmont Country Club

"The lightning bolt yesterday fried the irrigation system around the 17th hole and the driving range, so they've certainly had their challenges here. The head green keeper has done a great job. Green keepers from all over America come here to watch, to pick up tips. That's how highly Oakmont is rated."