Zach Johnson was not happy to hand his trophy back (see 13:55 BST).

He begins the defence of his title alongside Australia's Adam Scott and Sweden's Henrik Stenson.

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Patrick Reed leads The Open on his own as Haydn Porteous again feels the teeth of the back nine with bogey on 11.

Reed is not having his lunch or kickback relaxing, he's on the practice ground. He's game.

Jason Day has a putt of 40ft or more for par on 18, it snakes but comes up short, that's a round of two over. Not what the world number one had in mind.

Just 56% of greens in regulation and a total of 29 putts is not what we are used to.

Rickie Fowler was just two putts better off but at two under, is four blows better off on the scoreboard.

The final man in this three ball is Danny Willett. He can end under par here with a 10 footer... nope. Level for the day.

Oh dear Dustin Johnson. Driver may not have been overly wise there. The US Open champion is way, way, way right off the tee box. He may need to swim for that ball.

Martin Kaymer uses an iron but underestimates his muscles as an attempt to lay up sees his ball run into the bunker. Still, that's better than DJ.

Russell Knox, a Scot, he's seen this before, fairway.

Johnson is hitting another one so if they don't find his first ball that will be three off the tee.

World number two Dustin Johnson is the man in form. 

He won his maiden major title with victory at the US Open and backed it up with first place in the WGC Bridgestone Invitational.

Can he make it three-in-a row by winning The Open?

The American is joined by Martin Kaymer and Scotland's Russell Knox.

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McIlroy's birdie putt on the 17th has good pace, but not the accuracy, although he will still expect a par, which follows shortly after.

Meanwhile, Hideki Matsuyama rolls in a 10-footer and escapes only with a bogey after twice playing out of the rough.

Bubba Watson's tee shot was short of the green, and that costs him as he too drops a shot on the 17th. It is fair to say the American is not too happy with himself, muttering along in frustration.

It has taken 16 holes but Soomin Lee has finally dropped a shot. He is admirably pragmatic as he chips from trouble to 20ft from the flag. He could have gone for more but took his punishment and two putted. 

We have all been there on the course and thrown caution to the wind. Rarely does it pay off. Still, I'll still do the same next time.

Phil Mickelson with the trademark touch of the cap as applause rains down on him. Lefty rolled in a birdie from a healthy distance on two. Almost at the same time there are whoops from the galleries on 18 as Steve Stricker stiffs an iron to within a foot. That will be birdie and a four under round. A stunning finish.

Matsuyama chipped out of the rough, it finds the green, but the ball has a life of its own and runs off down the other side of the green. The world number 17 is certain to drop shots on the 17th.

As we've seen, Justin Thomas has already had a drink out of the Claret Jug.

Earlier this week champion Zach Johnson showed us the sad faces in his household as they waved farewell to the trophy he earned in a play-off last year.

Johnson is teeing off at 14:15 BST. He's a steady Eddie kind of player so who knows, he may win it back.

On to the par-three 17th and Bubba Watson looks furious with himself as his tee shot is well adrift of the green. But it is better from playing partner Rory McIlroy, who has left himself a birdie opportunity.

They've both done better than Hideki Matsuyama who is about to get acquainted with the crowd in among some pretty nasty rough.

We are back to shared leaders as Haydn Porteous cannot get up and down. He putts from off the green and races the ball past. He's unable to make the return. Back to five under.

The defending champion Zach Johnson is loosening up. One concern is that he has been sharing a house with some of the younger Americans like Justin Thomas. Let's hope the young bucks haven't been having too wild a time. I can't see any bags under Zach's eyes yet.

Three birdies, three bogeys for Hideki Matsuyama so far today. He has an opportunity for another birdie on the 16th, but can only watch on as he sends his putt to the right of the hole. Oohs and aahs from the crowd, a poker face from the Japanese.

Bubba Watson also misses a birdie opportunity, with his effort ending just agonisingly too short.

Rory McIlroy had missed the green earlier on, he got himself back in with a chance of a birdie and that putt looked good, before it fooled everything and drifted off late on. Pars all round on this one. 

On 18 Justin Rose can end the day four under with this lengthy birdie putt. It's downhill and breaks right to left. Looks a good weight, these greens aren't silly fast and so we have seen players have a go all day so far, aggression is the name of the game.

Rose is just off point and a par will see him end on three under. A fine round.

His playing partner Jordan Spieth ends the day level par with a dropped shot at the last. A frustrating round.

Watch three of the best moments of the day so far from a great chip to a hole in one.

The trio of Lee Westwood, Ernie Els and Phil Mickelson all made par on one. That looks like a great group to follow and we will keep you abreast of their movements.

Over on 13 Kodai Ichihara of Japan has just shown us the world's biggest follow through on a putt, his putter head ended up about about four feet off the floor after impact. It does the job as he nails a huge birdie. Absolutely huge, 50ft or more.

Rory McIlroy on the 554-yard par-five 16th misses the green, with the radar a bit off as he pulls his shot to the left, leaving him with a tricky up-and-down. He will need to pull some magic out of the bag on this one.

14:04 Dustin Johnson (US), Martin Kaymer (Ger), Russell Knox (Sco)

14:15 Zach Johnson (US), Adam Scott (Aus), Henrik Stenson (Swe)

14:37 Miguel Angel Jimenez (Spa), Jason Dufner (US), Marc Warren (Sco)

14:48 Anirban Lahiri (Ind), Sergio Garcia (Spa), Keegan Bradley (US)

Ben Dirs
BBC Sport at Royal Troon

In case anyone is wondering why most of the players are wearing two layers, well so am I. It's roasting out there, this seaside sun will take your face off if you don't take the proper precautions.

Martin Kaymer is applying sunscreen as we speak. He's off with Dustin Johnson at 14:04 BST. 

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Matt Jones is the latest player to fall victim to the 11th.

The Railway hole has seen just one birdie today, with players taking an average of 4.89 strokes on the par four hole.

So far it is statistically the hardest hole out there, with 24 bogeys and 13 players scoring double bogey or worse.