Ha! Robert MacIntyre hasn't had too much to smile about today at two-over for the round, but he shares a chuckle with Cameron Young after his pitch into the 18th just about creeps over the Valley of Sin.

Young tells the Scot he should probably run to mark his ball before it comes back down to his feet, and he takes the American's advice, much to the gallery's amusement.

Bob could do with popping that birdie putt in to make sure of his participation over the weekend...

The next man who Rory McIlroy is hoping to catch before the day ends has just been speaking to BBC Radio 5 Live...

After all that kerfuffle from Schauffele, McIlroy cracks on with his task.

The long eagle putt never looks like going in, but it doesn't have to.

A lovely knock sidles up close to the hole and that'll be another birdie.

Thank you very much.

Cameron Young has company. McIlroy joins him on 10-under!

Cameron Young did indeed make par at 17, and he's just short of the 18th green off the tee so he'll have a chance to cut Smith's lead to two.

Outshone by the other Cameron of course, but it's been an impressive round from Young. It's always difficult to back up a really low one but he's kept himself right up there.

Finally, it's game on.

Schauffele goes back to somewhere near the sixth tee and lobs one over the grandstand which, because it was next the gorse from where Schauffele wanted to hit out from, played a central figure in the row.

Lovely touch. That allows him to convert a bogey putt and minimise the damage.

Collin Morikawa, you've guessed it, misses another putt. His face looks like it has been set in cement.

You know the drill.

Thumbs up for YES

Thumbs down for NO

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Ok, we have a resolution. Xander Schauffele is told it is an unplayable lie and he must take a one-shot penalty.

Must say that seems the completely fair and logical decision.

From the ninth....

Image source, Getty Images

To the 18th

Image source, Getty Images

Alex Bysouth
BBC Sport at St Andrews

Collin Morikawa left with no choice but to play out almost backwards from the bunker - imagine being an average hacker trying to escape that?! Nightmarish.

Meanwhile, Rory McIlroy is trying to keep warm while they figure out what to do with Xander Schauffele’s ball - Radar has popped over to give the chilly-looking Northern Irishman an update.

My fault, shouldn’t have jinxed the weather by saying it was sunny…

While Xander Schauffele tries to his chat his way into a better solution, a penny for Collin Morikawa's thoughts.

The defending champion is down but he isn't out - yet.

He's still scrapping to beat the cut and has some time to mull over his next move - which isn't pretty either.

Talking of missing cuts... Morikawa's Ryder Cup team-mate Brooks Koepka is already cooked after a three-over 75 today..

"Ohhh no," cries Cameron Young after clipping his second out of the rough on 17.

It's short, but he's kept himself out of a really nasty spot. He'll have the Cam Smith putt over the slope, though, so we know how slow it is.

Ah, he's judged that really well and should have no problem tidying up for par.

"I've never hit out of a gorse bush. I don't know what the ball does. Honestly."

Candidate for the quote of the day from Xander Schauffele as he negotiates with the match referee about whether he can hit the ball or not.

Schauffele reckons it is not unplayable.

"I don't think that's reasonable," deadpans the official.

"You guys hit astonishing shots. But that would be an unbelievable shot."

-13 Cameron Smith (64)

-10 Cameron Young (16)

-9 Rory McIlroy (11)

-9 Dustin Johnson (67)

-8 Scottie Scheffler (68)

-8 Tyrrell Hatton (66)

Full leaderboard

Cameron Smith negotiated his opening 36 holes in 131 strokes.

That's a record for a St Andrews Open, with 132 having been achieved on three occasions before today: Nick Faldo (1990), Greg Norman (1990), Louis Oosthuizen (2010).

World-class.

Speaking of Norman, he's the last Australian to lift the Claret Jug. That was way back in 1993 at Sandwich.

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Oh dear. Someone pass a scythe to Xander Schauffele. He's in the deep doo-doo.

Officials are hovering around as the situation is discussed. Schauffele's ball is in the middle of a bush.

Twilight round, Al? Are they offering nine holes for a tenner? We're in.

Alex Bysouth
BBC Sport at St Andrews

It’s beautiful out here. Barely a ripple on the River Eden. Prime conditions for twilight golf, and a few more birdies…?

Suggest the 12th represents a decent chance for McIlroy to keep riding the Birdie Train.

A short par-four with a driveable green and plenty of birdies scored there today.

The Northern Irishman is swinging smoothly and confidently, nailing his tee shot and ending up on the short stuff.

Even think he's been slightly unlucky in that his ball should, by rights, have had a few more quicker revs to send it fully over the ridge on the front.

Anyway, he can't complain.

In other news, Schauffele hits the grandstand and Morikawa eats sand.

Cameron Smith cosies his birdie try down to beside the hole on the 18th and marks his ball. It's not going to be a 63, but it'll still be a flawless round of golf, and one that's catapulted the Players champion into a commanding position at the summit.

No bogeys to be found. The world number six leads by three.

His two playing partners haven't fared so well. Four-time major winner Brooks Koepka, who looks a shadow of his 2017/18 self, and Ireland's Seamus Power, who has featured in recent majors, will both be heading home after shooting 148 over the two days.

Image source, Getty Images

Alex Miceli
US golf reporter on BBC Radio 5 live

There seems to be something going on with Morikawa's game. He didn't make the cut of the Scottish Open and this week he's not playing well.

This golf course really has not been difficult for two days. You would think that he would do a little better than he's doing.

All he has to be do is be even par for goodness sake. He's the defending champion, he's won a couple of majors.

There is nothing to say there but surprise and wondering exactly what's wrong, because there has to be something not going right.