'Don't have the balls': Brooks Koepka hits back in naked photo controversy

World No.1 Brooks Koepka has taken a commanding position at the Tour Championship on the same day the first images from his naked photoshoot for ESPN's The Body Issue were revealed.

Koepka came under heavy scrutiny from golf commentators in March for losing more than 10 kilograms in preparation to be featured in the magazine next month, given it coincided with three poor tournaments.

But two US PGA Tour victories after the photo shoot - including the US PGA Championship - gave Koepka a direct passage to the season-ending Tour Championship, where he shares the lead after round one.

Koepka posted a 67 at the par-70 East Lake Golf Club on Thursday to climb to 10 under and he shares the lead with fellow Americans Xander Schauffele (64) and Justin Thomas (70).

In March, the muscular Koepka dropped from 95kg to 84kg and admitted it cost him 10 yards in driving distance.

It contributed to a missed cut and two other poor results at big events leading up to the Masters in April.

Former PGA Tour player-turned golf commentator Brandel Chamblee excoriated Koepka for committing "the worst self-sabotage that I have ever seen of an athlete in his prime".

But Koepka finished second to Tiger Woods at Augusta National before winning the PGA Championship, his fourth major title, in May and the elite WGC-Memphis event in July.

The 29-year-old hit back at criticism after Thursday's round one at the Tour Championship.

Shredded: Phil Mickelson shows off his physique in beach photo

"All these people that talk crap on social media; they don't have the balls to do (the shoot) and they wouldn't look that good," said Koepka, who is within striking distance of a $US15-million FedEx Cup bonus this week.

Koepka posted the first image of himself naked on social media on Wednesday night.

The Body Issue is a rebranded edition of ESPN The Magazine that features dozens of athletes in nude and semi-nude photographs.

"Getting naked's a bit weird; the first time you actually pull that robe off in front of 30, 40 people," Koepka said.

"It's something I wanted to do; to get chosen for that, you have to be one of the best in your sport."

Meanwhile, four-time major winner Rory McIlroy (66) is a shot behind Koepka at nine under.

McIlroy and Rickie Fowler supported Koepka's decision to pose nude.

"I know Brooks worked hard for that," McIlroy said. Added Fowler: "I think it takes some balls to do it, literally."

Meanwhile, Australia's Adam Scott posted a 68 to move to five under, while Marc Leishman (71) drained a 15-foot eagle putt on the 18th to finish at even par.