What an up and down day Collin Morikawa is having. Three over to one under, back to three over. And now he sinks a monster 35-foot putt on the par four sixth to pinch a shot back.

Justin Thomas nails a more routine birdie, as does Brooks Koepka to retain a share of the lead.

Three holes to go for the three Americans.

Early days but no surprise to see three Americans heading the leaderboard - the past six champions have all been from the Land of the Free and the Home of the Brave.

Lurking just behind them though are six Europeans, including England's Tyrrell Hatton and Matt Fitzpatrick.

How's your luck Tommy Fleetwood? He hacks out to five feet but can't make the par putt, overborrowing a fraction. Another shot gone for the Englishman.

Matthew Wolff's second shot found the front of the green, leaving a 50-footer which he rattled a good 10 feet past. And that's a great return putt, for just a third par of the round.

Phil Mickelson is trying to craft another magical chip from the back of the fourth green. Nine out of 10 for that one. Two feet left for a par.

Xander Schauffele from on the green, runs his putt three feet past. Par.

Rafa Cabrera Bello finishes off his front nine in style.

A delightful chip in from the rough to the right of the 18th green gives the 37-year-old Spaniard his first eagle of the day and bumps him straight up to tied for fourth. Cabrera Bello started on the 10th so he still has nine holes to go.

Americans may be hogging the top spot but there are now three Europeans hot on their heels, with Tyrrell Hatton and Martin Laird along for the ride.

Brooks Koepka just landed a putt from a mile away within a couple of feet off the flag. Obviously not a mile. But it was long. Easy par from there.

Justin Thomas showed how good it was, getting nowhere near as close with an effort from closer in. He miss a tough par putt and that's a bogey.

A disastrous hole, this 452-yard par four, for Collin Morikawa, meanwhile, as he signs for a double bogey. He had worked so hard to get back from three over - and now he's back at square one.

Tommy Fleetwood has only hit four of 12 fairways today. He found the last one and made double bogey...

From the middle of the sixth... "pulled it, pulled it, get lucky" he says.

When he says pulled it, he means it's about a yard left of the hole but, at a US Open, that's far enough left to mean trouble. His ball plunges second bounce into the cabbage and disappears. He's only about a yard off the green, but that looks an awful lie.

What a year it's shaping up to be for Marcus Armitage. First European Tour win, in contention at his second major, set a new world record...

That's right, the world number 122 secured another claim to fame with the farthest golf shot hit into a moving car at Elvington Airfield in April.

Armitage reached 303 yards when the ball landed in a car driven by Paul O'Neill, to surpass the long-standing record of 273 yards set by former Formula 1 driver David Coulthard and golfer Jake Shepherd in 2012.

Matthew Wolff has played 14 holes and he has just rolled in his eighth birdie of the day! Sadly for him, he's had three bogeys and a double. But he's back to where he was after five holes.

A setback for Tommy Fleetwood though, who makes double bogey despite hitting his tee shot into the centre of the fairway. He was long with his second, left his third in the rough, chipped out for four and missed a five-footer for bogey.

England's Marcus Armitage was understandably emotional after claiming his first European tour win at the 71st attempt in the European Open earlier this month.

He is looking cool as a cucumber at Torrey Pines today. The 33-year-old has just birdied the sixth - his 15th - to go one under for the day and take a part in 10th place.

Armitage started well with a birdie on his fourth hole but bogeyed his sixth. Hopefully he's back on track now.

It's going from bad to worse for 2014 champion Martin Kaymer. The German bogeyed the first two holes after the turn before hitting his second shot on the 12th even further into the rough. He ultimately came away with a double bogey.

And what's happening with 2012 winner Webb Simpson?!? The American has come in as the world number 12 but is now seven over after his seventh bogey of the day.

Many would have made him their pick heading into the weekend. Currently there's no-one worse off than the former champions on seven over.

And it seems to be catching. The 2019 winner Gary Woodland has bogeyed the last two to drop to one over.

Image source, EPA

A big leap up the leaderboard for Scotland's Martin Laird, who buries an eagle putt at the ninth hole.

It looked left all the way but the pace was just right, meaning the hole accepted it when it caught the lip.

It's worth a reminder of Brooks Koepka's recent US Open record given he ties the lead, even at this early stage.

2017 - 1st

2018 - 1st

2019 - 2nd

He didn't play last year because of a knee injury.

• -3 Rodgers, Koepka, Schauffele
• -2 Henley, Fleetwood, Wolff, Kim, Hadwin
• -1 E Molinari, Armitage, Migliozzi, F Molinari, Hatton

Brooks Koepka, now co-leader again after that Rodgers dropped shot, has a look at a putt on the fourth but it slides past, as does one from Collin Morikawa. Par for both.

If there was a prize for recovery pars, Justin Thomas would be a big contender. He dinks a cracking third shot out of the rough next to the green, then holds his nerve for the putt. He has rescued some pretty dire situations already today.

After back-to-back birdies on the 12th and 13th, Patrick Rodgers undoes all his hard work with a bogey on the 14th.

The American went way right of the fairway off the tee and a three-putt saw him get it down in five. Still, he's not doing bad given he's at his third US Open.

Over on the second green, Phil Mickelson barely taps the back of his ball and watches as it trundles 25 feet down the hill and a couple of feet beyond the hole. Par

From slightly closer in Xander Schauffele can't trouble the hole either. He too settles for par.

Seems madness that a 493-yard hole is a par four but that's modern golf for you!

When you can drive it 330-odd yards like this trio, I guess it's hard to argue.

Brooks Koepka and Collin Morikawa are on the green in two, putting that shocker of a par three behind them. Justin Thomas, though, has overshot the green - everything is a struggle for him at the minute.

Neil Matthews: No, a 'feud' (real or staged) between two leading golfers isn't 'good for the game'. It's about as edifying as two bald men fighting over a comb. Golf has gained its reputation through players who behave like grown-ups. Let's keep it that way.

Neil Matthews is pretty certain of his view on the social media spat between Brooks Koepka and Bryson DeChambeau. Let us know what you think using #bbcgolf on Twitter.

Tommy Fleetwood is putting together a superb round of golf. He went close to winning this title at Shinnecock in 2018, when he closed with a 63 - the first player to go that low at a US Open. He ended up one behind winner Brooks Koepka.

Anyway, a fourth successive par leaves him handily placed after 13 holes.

Playing partner Matthew Wolff is continuing his crazy round. A bogey on the third has been countered with another birdie on the fourth.