KIAWAH ISLAND, S.C. — Quietly, this has been coming for Corey Conners.

On Thursday, in the opening round of the PGA Championship at Kiawah Island’s daunting Ocean Course, Conners played one of the best rounds of his career, shooting a 5-under 67 to take the lead into Friday’s second round.

He’s the first Canadian to lead a round in a major championship since Mike Weir led the 2009 U.S. Open.

Conners leads a group of six players at 3-under that includes Brooks Koepka, Keegan Bradley and Viktor Hovland.

Defending champion Collin Morikawa, Phil Mickelson, Cameron Tringale, Martin Laird, Gary Woodland, Branden Grace and Kevin Streelman are among the players at 2-under.

While player after player came off the course looking drained and speaking of how stressful it was out there, Conners looked pretty cool, calm and collected afterward. His card looked pretty stress-free — six birdies and only one bogey.

“I’d say it’s impossible to be stress-free around this golf course,’’ Conners said. “You can’t fall asleep out there on any holes. It’s very challenging. I was fortunate to have a good day [and] made it as least stressful as possible on myself.

“It was a really special round. I did a lot of things really, really well. I hit a lot of really good shots and holed some nice putts early in the round, and that really helped boost the confidence.’’

Conners entered the week having had four top-10 finishes in 2021, including a tie for eighth at the Masters, a seventh-place finish at the Players Championship and a third at the Arnold Palmer Invitational — all high-profile tournaments with stout fields.

But this is new territory for the 29-year-old, who’s playing in his ninth career major championship. In his previous two PGA Championships, he has a tie for 64th in 2019 and a missed cut in 2020.

“I kind of started the day thinking, ‘Why not me? There’s birdies to be had. Just play,’ ’’ Conners said. “I am really pleased with the score. I definitely knew in my preparation that it was possible to have a decent round out here and shoot a 5-, 6-under-par round. Just play with patience, take advantage of opportunities when they present themselves.’’

On a day when the Ocean Course ate the lunch of some high-profile players (Rory McIlroy and Justin Thomas shot 75, Adam Scott a 78), Conners did just that.

“It was not easy out there,’’ Bryson DeChambeau said after shooting even-par. “Mentally, you have to show a lot of resolve out there — mental fortitude to just push on when things aren’t going well.’’

It surely sounded like Conners had a very different day than the likes of DeChambeau or McIlroy, Thomas or Scott.

“I definitely felt calm out there,’’ he said. “It was fun. It’s fun to hit good shots; it’s fun to give yourself birdie chances and fun to roll in putts.’’

As the week goes on, Conners will do well for himself to keep thinking, “Why not me?’’

“Definitely I have a lot of belief in myself, and I’ve been playing well for quite a while,’’ he said. “I’m excited for opportunity to play against the best players in the world and put my game to the test. I have a lot of confidence in my game and I’m excited for the rest of the weekend.’’

The leaders emerging from the early wave of tee times included Bradley, the 2011 PGA winner, and Koepka, the 2018 and ‘19 PGA winner who began his day with a double bogey on his first hole, the 10th.

“It wasn’t ideal, the start,’’ Koepka said. “You can’t do that stuff if you want to win. You’ve just got to be more focused. I don’t know if that’s a lack of not playing [because of knee surgery] or what. I don’t know. It was just stupid. A poor club choice off 10. So mental mistake there. [I] deserved every bit of that double bogey.’’

The gaffe, though, “helped get the round going and got me focused,’’ according to Koepka, who played his final 17 holes in 5-under par.

Bradley had a different experience than Koepka in that he felt in the zone as soon as he hit his first shot of the day.

“I hit the ball about as good as I can hit it,’’ the former St. John’s star said. “Some days you get out there and you go, ‘I’m going to aim it at that tree and draw it off that tree,’ and it comes right up off that tree and does what you think. Today was one of those days.’’

No one, of course, had a better day than Conners.