Charlotte, N.C. — If Jordan Spieth needs some help with the mental aspect of his game during this pressure-packed week of golf, he knows exactly where to turn.

Michael Phelps is right there for him.

Phelps, a 23-time Olympic gold medalist who knows a thing or two about performing at his best under crushing pressure, spent Thursday following Spieth around Quail Hollow during the first round of the PGA Championship. The 24-year-old Spieth is looking to become the youngest player to win golf's career Grand Slam.

Spieth was thrilled to have Phelps inside the ropes with him.

"He's become a good friend and even a mentor," Spieth said. "That's pretty awesome to have a mentor like that."

Phelps and his wife Nicole Johnson followed Spieth, U.S. Open champion Brooks Koepka and Masters champion Sergio Garcia for most of the round, mostly staying out of the way but always visible.

It's not the first time Phelps has shadowed Spieth around the course.

Phelps, an avid golfer, struck up a friendship with Spieth last year in Phoenix through their mutual sponsor, Under Armour. They've hung out together in Cabo San Lucas, where they had a photo taken with former NBA great Michael Jordan, golfer Fred Couples and NFL players Russell Wilson and Dwight Freeney.

Phelps has also tweeted well wishes to Spieth after his victories.

"We have had dinner and talked through a lot of things," Spieth said.

Spieth said the specifics of those conversations are private, but said the conversations focused around "a lot of mental approach and preparation and stuff."

Phelps did not speak to reporters on Thursday.

Spieth said at a post-round press conference at the British Open that he felt like he could call Phelps any time for advice — and that he'd be doing himself a disservice if he didn't, given Phelps' past success in swimming.

He might need some of Phelps' advice on the mental part of the game if his putting doesn't improve on Friday.

Normally one of the game's best on the greens, Spieth said he "can't putt any worse" than he did on Thursday. Still, he avoided big mistakes and rallied with birdies on two of the final three holes to shoot a 1-over 72, leaving him five shots behind early leader Thorbjorn Olesen.

Phelps, who was recently seen racing simulated sharks on the Discovery Channel, joked around with Spieth's caddie Michael Greller on the first hole. Spieth said it helped ease the tension.

"He kept it light," Spieth said.

Spieth said he was delighted when Phelps texted and told him he would be in Charlotte for the PGA Championship because of a sponsorship commitment.

Phelps isn't the only celebrity who has been in town for the city's first major championship.

Singer Justin Bieber attended the practice rounds earlier in the week, while Darius Rucker performed in the area on Wednesday night and was joined on stage by former PGA champion John Daly. Roy Williams, the coach of the defending national champion North Carolina men's basketball team, was also seen at the first round on Thursday.