Iain Carter
BBC golf correspondent on BBC Radio 5 live sports extra

The putting is the difference for Zalatoris and why he's not a winner at Tour level yet.

Pereira looks like a cool customer on the greens, as he needs to hole something around six feet to save his par.

It's a damaging three-putt for Zalatoris though, as he misses his par save from no more than four feet.

Zane Scotland
Former European Tour player on BBC Radio 5 live sports extra

Pereira looks like he's ready to rock 'n' roll. He's definitely up for this today.

What. A. Shot.

Matt Fitzpatrick is in bother on the par-five fifth after pounding his approach into the sand but that's different gravy. He chips out and has barely lifted his head above the greenside bunker as his ball arrows into the cup.

As nonchalant as you like he shakes off the sand from his shoes and heads off to the sixth with barely a flicker of emotion as the gallery roar their approval.

It doesn't drop for Rory. Nothing has so far, but he jabs in from a putter's length for another par.

Ancer has four feet to gobble up for his first birdie of the day and makes no mistake, bobbling it in!

He moves to five under.

Our leaders both don't hesitate to pull out the big dog and have a slash at the short par-four fourth hole.

That's the modern way, as there's no thought of just placing an iron down there and wedging it in close, but it's not quite worked out for them.

Pereira is in the trees on the right and just has to dink it out short of the green, while Zalatoris gets a nice break off a cart path, but then his chip out of the rough flies to the back of the green.

How about that from Abraham Ancer, a beaut of an approach that heads right for the pin and settles a few feet from it. Big birdie chance on the way...

Rory McIlroy is also on the smooth stuff but will have to work a little harder for his first birdie of the day.

Ryan Fox finished in a tie for second on the DP World Tour last week, and that form is carrying over as he's just sneaked into the top 10 here with a birdie on 13.

It's a third birdie of the day for the New Zealander.

A mammoth par five this, Rory McIlroy still has 340 yards to the pin after his drive and leaves his approach shy of the green. Abraham Ancer hits a lovely little stinger that never veers above the tree line, very satisfying.

Oh hello. Birdie, birdie.

JT sets the ball rolling draining a putt from 17 feet for a three and Bubba Watson follows suit after a wonderful chip on to five feet.

Both have played pretty well so far. Are their putters starting to warm up as well.

Zane Scotland
Former European Tour player on BBC Radio 5 live sports extra

It's definitely a good thing they're playing together. They don't have a big star like a Rory McIlroy who attracts the big crowds. It's the pairing they would want at this point.

Pereira has a dig from 24 feet but the putter can't work its magic this time around as he flies it way past the hole.

He leaves himself a stinky three-footer which he does well to hole.

Speaking of stinky putts, Zalatoris has a glorious birdie chance but it goes straight right off the face and never has a chance.

Laurie Canter's round draws to a close. The Englishman's card looked pretty good after the front nine where he made four birdies against two bogeys.

However, a greenside bunker cost him a shot on the 14th and he ends with another dropped shot on the 18th.

Huge misjudgement from Bubba Watson on the third.

The American has a fiddly little close-range chip onto the green but doesn't get enough juice on it and sees it roll back down the slope to leave another shot from just off the putting surface.

As Justin Thomas tidies up for par, his playing partner plots his next move, which means the putter comes out. Watson's nudge up towards the cup turns off left as he drops a shot.

McIlroy pops on with his second at the fourth after that drive that came up short and right of the green, leaving himself an 11-footer for birdie... it wriggles left of the cup, he needs one of those to drop. Four pars to start.

Zane Scotland
Former European Tour player on BBC Radio 5 live sports extra

Rory needs to get a birdie in early and get the momentum going.

Mito Pereira, in his first US PGA Championship, is now the solo leader at Southern Hills after dropping a bomb on the second green.

The man from Chile lands a 30-footer to move to nine-under, and Zalatoris is then suddenly under huge pressure with his seven-footer for par.

He drains it though to stay just the one shot behind.

There's no way Bob MacIntyre could have envisioned his implosion today.

The Scot played the first 36 holes at one over but is nine over today and the way things are going he'll be propping up the leaderboard by the time he heads into the clubhouse. What an absolute shocker so far.

Right, will Rory McIlroy take on the green here? It's 373 yards, down wind... he'll give it a decent crack. That catches the rough on the right, leaving him 35 yards from the pin.

There's hardly an ounce on Will Zalatoris' slender frame, by boy can he send it out there off the tee - with another drive over 300 yards at the second.

The speed he gets through the ball from unwinding is quite something, like a coiled spring.