Martin Kaymer is on a great run, and is now the highest ranked European as a birdie on the 10th, his fourth in five holes, takes him to four under, one shot behind leaders Patrick Reed and Phil Mickelson.

Dustin Johnson does well to save par on the par-four 10th after pulling his second shot wide.

Rory McIlroy had a couple of holes to forget which ultimately cost him today. Watch as things went very wrong on the 13th and 14th. 

You are in effect shooting into the dark on the 10th tee, with high banks obscuring your view of the fairway.

Dustin Johnson, Russell Knox and Martin Kaymer all do OK though, with their first shots either on, or close to, the fairway.

Johnson did OK with shot one, but he hates shot two as he pulls it left, missing the green in the process. He may well be dropping back to level par soon.

Eight pars on the trot, and then a birdie for Adam Scott on the ninth sends the Australian into the back nine on one under.

This is where the tricky stuff begins for the 2012 runner-up.

-5 Patrick Reed (18), Phil Mickelson (10)

-4 Justin Thomas (18), Steve Stricker (18), Justin Leonard (13), Zach Johnson (8)

-3 Justin Rose (18), Soomin Lee (18), Shugo Imahira (18), Richard Sterne (18), Tony Finau (17), Justin Leonard (14), Martin Kaymer (9)

-2 18 players including Rickie Fowler (18), Rory McIlroy (18), Ernie Els (10), Henrik Stenson (8), Sergio Garcia (5)

Selected others:

-1 Bubba Watson (18), Padraig Harrington (18)

E Colin Montgomerie (18), Jordan Spieth (18)

+2 Jason Day (18)

+3 Jim Furyk (18)

View the full leaderboard here., external

Will this dominance continue?

Patrick Reed is clubhouse leader on five-under, Phil Mickelson shares the lead after 10, while the first seven spots on the leaderboard are filled by Americans.

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Watch as Phil Mickelson hits a sublime tee shot on the famous Postage Stamp. 

Tony Finau is one of those Americans in contention on day one, with the 26-year-old completing his first round at Royal Troon in a four-under 67.

Finau was a model of consistency, carding four birdies and not making a single bogey - impressive, considering what had gone before him on that back nine today.

Like a rainbow.

A skewed tee shot sees Martin Kaymer miss the fairway on the ninth, but it does not do him too much damage as he has a nice lie and can plonk his next shot back on course. 

He is then at the far edge of the green and his speculative attempt for a birdie is inches wide. His run of birdies, which stood at three, comes to an end but a par keeps him on three under.

Dustin Johnson, with a gentle right-to-left, underhits his shot for a birdie and also walks off with a par.

That is a two for Zach Johnson at the par-three Postage Stamp, moving the 2015 winner to four under par through eight holes.

And that means the current top seven in this year's championship are now all American.

Any danger of denting this US dominance, rest of the world?

Image source, Getty Images

BBC Golf commentator Andrew Cotter’s brother Colin is caddying for South Korean Soomin Lee at this year’s Open. Lee finished with an impressive opening round of 68 to finish 3 under par and Colin has been chatting to John Inverdale on BBC Radio 5 live.

“I’ve never caddied for him before. We’ve had three practice days before today, that’s it. 

He struggled on the first practice day so I just left him to it, but by the end of the day I was feeding him the odd bit of info and advice.

I think we’re both fairly comfortable with each other now. Hopefully I’ll give him local knowledge.”

The Open is live on BBC Radio 5 live. Listen here.

Not sure this is in the R&A's rule book.

No messing around from Phil Mickelson, he continues the par-birdie-par-birdie sequence set on the front nine with a birdie on the 10th.

And that takes the American into a share of the lead with compatriot Patrick Reed.

Henrik Stenson is a few holes further back, with the Swede having eagled the sixth before missing a birdie chance at the seventh.

Defending champion Zach Johnson also fails to convert a birdie opportunity on the par-five, which leaves him on three under.

Dustin Johnson lets a birdie opportunity slip through his fingers on the eighth as his 30 foot putt clips the edge of the hole and stays on the grass.

Kaymer is next to have a go, and shows Johnson how to do it. Three holes, three birdies for the German, who is up into the top 10.

No such joy for Russell Knox though, but the Postage Stamp does not prove too tricky and he, like Johnson, leaves with a par.

Oooh, was that good or bad luck for Sergio Garcia there? He plays out the bunker and hits the flag, which may have stopped his ball fizzing away across the green.

The Spaniard has birdied two of his opening four holes, putting him on two under.

We want your John Daly-esque clobber and you are delivering.

Watch your eyes!

On to the Postage Stamp eighth and Martin Kaymer, fresh from two successive birdies, has a chance for a third after a delightful shot off the tee.

Dustin Johnson and Russell Knox also follow him on to the green.