Cameron Smith tops the Australian challenge at the PGA Championship at Valhalla, where American Xander Schauffele recorded a course record 62 to sit 9-under with a three-shot lead over Sahith Theegala, Tony Finau and Mark Hubbard.

Signing for a 3-under 68 and share of 18th, Smith made four birdies against one bogey during the opening round, with Lucas Herbert also under par at the year’s second men’s major after a 2-under 69.

Jason Day is the next best Australian at even-par, one in front of Adam Scott and Min Woo Lee, with Cam Davis rounding out the Australians on 7-over. Kiwi pair Ryan Fox and Kazuma Kobori, the reigning Challenger PGA Tour of Australasia Order of Merit champion, opened with 1-over and 2-over rounds respectively.

Starting his round on the 10th tee, Smith got to work early with a birdie at the long par-3 11th before making the turn in 2-under courtesy of another birdie at the par-5 18th.

The Queenslander added more birdies at the third and fourth to reach 4-under, and a spot in the top-10, before his lone bogey of the day came at the fifth after his drive found the native area.

“I actually hit the ball quite well. Probably the first 12 or 13 holes there,” Smith said.

“Kind of let go of it a little bit at the end, but everything felt really good. Managed to get a few good par saves and kind of keep the momentum going for tomorrow.”

Among those momentum maintaining pars was Smith’s going without his shoes and socks to strike his second shot at the par-5 seventh on the way to an unlikely five.

The major champion headed for the driving range followed by some rest on Thursday afternoon ahead of what could be a long tournament with rain predicted for much of the week in Kentucky.

“It's going to be a long week. I think you know that at the start of the week anyway. It's a major week,” he said.

“It's always more demanding, so plenty of rest this afternoon. Maybe get a few balls, clean some stuff up and yeah, get a good sleep tonight.”

The first Australian on course, Herbert’s round got off to a rocky start when the Victorian bogeyed the par-4 10th, his opening hole of the day.

Another bogey at the 256 yard par-3 14th was an ominous sign, before an impressive fightback from the 28-year-old who made four straight birdies starting at the 15th before an even-par back nine left him tied for 32nd.

“I think everything was kind of decent, but nothing was amazing,” Herbert said.

“I think I holed out really well, holed some sort of nice five-footers, five sort of eight-footers just to keep momentum through the round.

“Obviously got off to a poor start there, but then caught that back up with four birdies. So just to keep that momentum going through the back nine and not drop any shots.”

Like Herbert, Day opened his account with a bogey in a front nine where pars were rare for the 2015 champion, who made three birdies against three bogeys to turn in even par. The Queenslander was yet another to drop a shot at the long 14th before birdie at the 18th for even-par would have made Day’s dinner taste a little sweeter.

Playing alongside Tiger Woods, Scott experienced a frustratingly consistent day where he made 17 pars, failed to make a single birdie and dropped a shot at the 14th, while Lee fought back from a 17th hole bogey with a birdie at the last to join Scott in T85.

Davis, who was without a birdie in his 78, has his work cut out in the second round to make the weekend.

Making his major championship debut, Kobori will no doubt be proud of his 73 on the game’s biggest stage, while compatriot Fox leaked oil in a bogey-bogey-double stretch from the 11th before righting the ship with birdie at the last.

The PGA Championship is live on Fox Sports, available on Foxtel and Kayo