In the peculiar world in which he now finds himself, Henrik Stenson is like a man among Mouseketeers.

Pro golf, you see, got all caught up in a youth movement this season, and where does that leave a 39-year-old campaigner who still looks fit enough to model any sort of European cut he may fancy? Stenson came into this Tour Championship a lofty fourth in FedEx Cup points, and yet with all the attention paid the 20-somethings, you couldn’t be quite certain whether he was a competitor or the chaperone.

“Yeah, it’s been a lot of Jason and Jordan and Rickie and Rory,” Stenson said with a wise smile, “so, of course, it’s good to get a good start and hopefully we can progress from here this week.”

This time it was Stenson — proclaimed Mr. September in one golf magazine when he won the FedEx Cup in his only other trip here in 2013 — who seemed intent upon draining the suspense from a golf tournament almost before it started. Stenson shot a front-side 29, one off Tiger Woods’ course record, on his way to a first-round 7-under 63. He was two shots clear of Paul Casey.

The guy who’s had the job of suspense-killer in recent weeks, Jason Day, decided to show his human side for a day. Cut him, he does bleed. Send his tee ball into the sylvan abyss, and he does take triple bogey.

Like Day, Stenson birdied the first three holes he saw Thursday. Unlike the new No. 1 player in the world and the No. 1 on your FedEx Cup point standings, Stenson didn’t feel the need to drive one so deeply into the woods on No. 5 that it would have required at least four Eagle Scouts to rescue it.

Day still managed to finish under par with a 69, but that number looks pale and wanting for a player who has won four of his past six tournaments, many of them by comfortable to cavernous margins.

And now it was his turn to be impressed by the number atop a leaderboard. “I know this course is very difficult,” Day said. “I didn’t expect to see Henrik shoot 7 under. He could possibly have gone lower, but I didn’t see that.”

It was a grand day for relative geezers. Zach Johnson, the oldest player in the field by less than two months over Stenson, shot 66. He alone had the only bogey-free round of the day.

Otherwise, things were a little rocky for the A-Flight of the Tour Championship (that being the top five in points, the ones who win the FedEx Cup, no questions asked, with a tournament victory). Jordan Spieth (68 on Thursday) was five back, Rickie Fowler (69), Day six back and Bubba Watson (70) seven shots in arrears.

Stenson — “So very pleased with the start; I couldn’t have asked for anything more, really,” — was understandably buoyant after the round. That smile he wore coming off the course belonged to a player who seemed to know secrets about East Lake and about the FedEx Cup system that no one else did.

His wily veteran savvy was a big part of the day. For one, Stenson quarantined his driver, all but taking it out of his bag and sending it to a CDC isolation area.

“The biggest threat to a player is the rough around here,” he said. “If you miss the fairway, I would say it’s a very high percentage you’re going to miss the green from there on as well. Hitting fairways is definitely crucial and I feel like I gave myself the best chances with 3-wood and 4-wood on a lot of these holes.” Stenson was tied for second in the field, hitting 11 of 14 fairways.

Stenson is the one player among the top five in points who has not won a tournament this year, and the sly fox had no regrets about possibly gaming the system.

There are reasonable scenarios out there — especially if Day does not make a big move — that would allow Stenson to win the $10 million FedEx Cup bonus even if he doesn’t hold his lead.

“If I were to finish second and win the FedEx Cup, I’m pretty sure I’ll be smiling on Sunday,” he said. “I’ll be smiling more if I got two trophies rather than one, but I’ll deal with one as well.”

So very adult of him.