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Rory McIlroy is on the first tee just as Justin Thomas drains a putt on seven to move to five under and into sole lead.

We have co-leaders again as Kevin Chappell keeps his fine start going with a birdie on eight. He moves alongside Justin Thomas.

Suddenly we have four men on four under as Patrick Reed and English amateur Scott Gregory make birdies. We will bring you more on Gregory shortly. He's having a dream round.

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If you are just joining us, Colin Montgomerie was the early story of the day. On his home course he endured a nightmare opening hole and then went birdie mad to lead on three under.

He's given one back now but saves par with a colossal putt, it must be 50ft, on 13.

Monty is doing himself proud as the young guns now out on the course set about stealing his limelight.

It's worth nothing our two Team GB male Olympians are out there now. Willett and Rose are Rio bound.

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Danny Willett up first, white trousers very much in vogue and all three in this group have them on show. Unlike many others, Willett has the driver out and that is huge, right up the middle and just short of the green. This is a par four remember. Willett has brought birdie into play big time.

Rickie Fowler goes with iron, he's been under the weather this week, solid start, fairway.

And now the world number one. The usual step back to look down the line, Day is big on visualisation. He goes with iron and it's good.

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The second hole, Jordan Spieth is firing out of the rough. He can't go at the flag due to a bunker so runs one up, skirting the sand trap and that is superb, it leaves 15ft for birdie. Justin Rose is just as good with a more direct approach but Shane Lowry will need his spade I'm afraid. The bunker has him trapped.

Now, to tee one...

The world number one Jason Day is about to tee it up with Rickie Fowler and the Masters champion Danny Willett. Three minutes and counting.

"This is pretty special," says Day. "The greats have all held the trophy, the Claret Jug. To be able to hold that once in my career, it would be very pleasing and satisfying. 

"I get excited to be able to play the Open Championship because of how challenging the golf course is and the weather."

"This is a very, very special tournament, everybody knows that," says Jordan Spieth.

"I crave to have that trophy in my possession at some point, and to reach a third leg of the Grand Slam this week would be a fantastic achievement and a life-long goal of mine." 

Spieth cannot sink a 10 footer on one. Unusual for the man who tends to putt with the efficiency of a German factory line. Justin Rose also makes par.

Byeong Hun An is suddenly in need of protective gloves, that's how hot his putter is. 

He snakes one in from 35ft or so on the fifth, it takes the break wonderfully and drops. He's just one off leader Justin Thomas now on three under.

What about Shane Lowry? He of course led on the final day of the recent US Open but saw his dream disappear on a horribly difficult Oakmont course.

Lowry won the WGC Bridgetsone Invitational last year, a big tournament, so he knows how to get it done.

He has a birdie putt on the first, it's 15-20ft. Great effort, just wide. Par.

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Some of you may recall that Jordan Spieth came into this event last year as Masters champion and US Open champion. There was talk of a clean sweep of majors.

When his chance disappeared late on Sunday, the share price of his sponsor Under Armour took a dive. That's right, Spieth moves markets.

Take a look here.

-4 Justin Thomas (5)

-3 Marcus Fraser (9), Sanghee Lee (9), Scott Gregory-a (7), Jim Furyk (5), David Lingmerth (5), Patrick Reed (4)

-2 Colin Montgomerie (11), Alex Noren (6), Kevin Chappell (6), Byeong Hun An (4)

Patrick Reeds follows up an eagle on three with a birdie on four. His putt is firm and running at pace, it tries to loop around the hole but gravity is Reed's friend on this occasion.

And so to this wonderful three ball. Jordan Spieth up first, iron, whisks the ball of the tee, twirls the club, fairway. 

Justin Rose, shades on, white cap, iron, big divot, into the semi-rough. 

Shane Lowry, white cap, white glove, black long-sleeve top, steadies himself, iron, fairway all day long.

I like this group. Class written all over it.

McIlroy, Willett, Bubba and Fowler all up soon too. We are rolling.

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Byeong Hun An shows us what eagle looks like. Both he and Patrick Reed have done that so far today. The South Korean drops a long putt across the green and walks away with a nod, little emotion. 

We have a fizzer of a group on the first tee. Justin Rose, Shane Lowry and Jordan Spieth.

Come on Monty, dig in and scrap sir. Three putts on 11 see him drop his first shot since the opening hole. Bogey.

Those of you who joined us early today may have seen me mention how wise Luke Donald is to wear a visor and give his hair some room to breathe. 

Justin Thomas, aged 23, has gone the other way.

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Philip Stothers: Monty's on fire, Troon's greens are terrified! Oh na na na na na...! The new Will Grigg.  

Monty's certainly started well. Don't think Royal Troon would be happy with football chants though Philip!

Sam Harris: Not a clue who Sanghee Lee is, however he was 750/1 pre tournament. I wonder what odds he is now?!

Well he's 24 years old from South Korea and is currently ranked 346th in the world. His odds are now as short as 150/1!

Tweet us your thoughts at #bbcgolf on who you think will win, whose caught your eye at this early stage or maybe just tell us how much you love this great tournament.