That's remarkable! From 114 feet, Hovland judges the pace beautifully and gives himself a good chance to save par.

These little par putts, they're what make a champion, and Hovland slips his in the left edge. A truly superb two-putt.

McIlroy fancies this one. It's actually closer than I originally thought at 16 feet. Nope, he hasn't hit that one at all.

Maybe he didn't fancy it, but he rolls it home for a four and the co-leaders stroll towards the par-five 14th.

First up on the 12th green is Cameron Young.

He gets a bit overexcited with a long eagle putt, ball racing past and leaving a tricky one back.

Luckily, he can first watch and learn from Cameron Smith's almost identical putt.

Smith's ball doesn't drop, leaving him curtly cursing. Sound like a broken record but his putter is really not firing today.

What can Young do? He can confidently can it. Into outright third!

Looks like Cameron Smith finds himself in a similar spot to where Rory McIlroy was a few moments earlier.

Down in front of the green with a ridge lurking on the right and ready to spit the ball away from the flag.

Luckily he's a dab hand with the wedge and gives himself another birdie putt.

Hovland's approach to the 13th is coming in hot!

Deary me. He's a mile from the flag. That'll be a full swing with the old Texas wedge there.

McIlroy sends his in much tighter, but it takes a firm first bounce and skips on by to around 25 feet.

Kat Downes
Commentator on BBC Radio 5 live

You cannot take anything for granted as Dustin Johnson didn't give it the rap it needed and he is now four off the lead.

Par for Scheffler but it's Johnson who drops a shot this time as he misses a seven-footer for his par and he too slips back to 11 under now as they head to the second par five.

The final pairing both drove the green on the ninth and the 12th - another short par four - offers another opportunity to swap the big dog for the short stick.

Oh behave! Cameron Young hits a beauty of a drive and will do just that on his walk up.

"That's the shot of the day," says Laura Davies. Who are we to argue with a golfing dame?

Can Cameron Smith follow suit? Not quite. He's doesn't have the same power off the tee as his namesake, but he's not far off.

Alex Bysouth
BBC Sport at St Andrews

“Here we go, Rory boy!” cheers one fan as the co-leader gets to soak up the adulation of the fans around the tee box while Viktor Hovland takes a quick comfort break - like a tennis player at Wimbledon, maybe he’s just using it as a moment to refocus.

Hovland is then forced to wait down with us media by the gorse bushes while Rory drives almost over our heads… he chuckles at the prospect.

McIlroy's out with the three wood on the 13th. If there's one club that's stopped him from winning more tournaments in recent months, it's this one.

And he winces as he sends it into the stratosphere. It scurries towards the gorse bushes, but thankfully stops short and rolls back down into the first cut. Not a bad position by any means, that.

Hovland smacks his driver and finds the rough, but the lie looks decent. Danger avoided.

McIlroy's birdie putt looks good - it burns the right edge! He can't believe it.

Just a par.

Hovland has a great chance to retake the lead on his own. Ah, his putting deserts him for once, missing it low and left.

No change.

Surely one of the best feelings in the world of golf? Grabbing an eagle on the last on the Old Course at St Andrews.

Regular major challenger Xander Schauffele does exactly that, finishing an up and down round with the ultimate high.

McIlroy faces a treacherous chip at the 12th. There's just no chance of getting it in tight, but he makes a decent fist of it and at least he'll have an uphill look at birdie.

Hovland from the rough. Ohhh that's magnificent, using the slope to perfection and his ball trickles down to around 12 feet from the pin.

Alex Bysouth
BBC Sport at St Andrews

Down by the 12th green you see the players on the tee swing and then you hear the crack of the driver on ball. Rory has sensibly stuck his jumper on with the breeze making it a tad chilly down this stretch by the river.

We've said it time and time again - you MUST stay out of these bunkers, as Scheffler's visit costs him a shot on the 12th.

DJ pars it to remain on 12 under as his compatriot slips back.

McIlroy's staying loose as he waits for the Johnson-Scheffler group to finish up on the 12th green, taking a few practice swings with his driver.

Johnson sauntering off the green is the signal for McIlroy to have a cut at it.

Smack! He hasn't quite caught that one on the sweetspot and it comes up short of the bunker - shame, he probably wouldn't have minded some more play time in the sand.

Hovland sends his down the left and it gets caught up in the rough. That'll be a tricky pitch from there.

Young putts first, coming from the opposite side to Smith and having to deal with a big right-to-left swing.

Difficult one to control and the American debutant comes up short with his birdie putt.

Much better chance for Smith. Slightly downhill but with little movement from either side.

He aims a tad to the left and the ball doesn't move from its line.

A pair of pars.

James Bamford: Hell's teeth Rory! This is already a classic Open. No idea who is going to win.

Very few players have managed to attack the 11th flag today... but Cameron Smith does.

The Aussie is bang on the money. Ball lands within the red zone and just skips to a halt about 15 feet away on the par three.

Image source, Getty Images

Scheffler gets stuck in an awkward spot in the bunker just short of the 12th green, it's pretty close to the face but luckily enough he has a shot to advance it and can dig it out just short of the green.

From there it's a tough putt as there's a huge slope just after the hole, and sure enough the ball scoots on and leaves him a tough par save.

That looks like a fair bit of kit for Kat to keep control of. And a real shame the chocolatey treat hasn't survived the warm conditions here on the coast.

Tune in to BBC Radio 5 Live coverage via this very webpage. The next couple of hours promise to be quite something.

Image source, BBC Sport