ROCHESTER, N.Y. -- About the only thing Bryson DeChambeau has transformed more than his golf swing during his career has been his body. After bulking up to hit the ball farther off the tee a few years ago, DeChambeau has slimmed down considerably to conserve energy.

That change, along with a series of others, finally led to some positive results in the opening round of the PGA Championship at Oak Hill Country Club on Thursday. DeChambeau had six birdies and two bogeys and took the early lead with a 4-under 66.

"The emotions have definitely fluctuated pretty high and pretty low, thinking I have something and it fails and going back and forth," said DeChambeau, the former No. 4 player who has since fallen to No. 214 in the Official World Golf Ranking. "It's humbling. Golf, and life, always [has] a good way of kicking you on your you-know-what when you are on your high horse. It's nice to feel this today."

DeChambeau, who says he weighs between 210 and 215 pounds, has changed his diet from a daily intake of 5,000 calories to about 2,900. He has stopped eating foods that inflame his body, including corn, wheat, gluten and dairy products. DeChambeau said he lost 18 pounds in 24 days after he started the diet in August.

"It was crazy," DeChambeau said. "It wasn't fat. It was all water weight. You know how I looked before. I was not skinny."

Those weren't the only changes DeChambeau made in his life. The 2020 U.S. Open champion jumped from the PGA Tour to LIV Golf, where he is captain of Crushers GC. He changed his equipment company, caddie and swing coach as well.

Through increased strength and swing speed, DeChambeau once believed he could conquer professional golf with brute force. He once boasted about Augusta National Golf Club, the site of the Masters, being a par-67 course because of how far he was hitting balls off the tee. He entered national long-driving contests and performed well.

Even after losing considerable weight, DeChambeau averaged 313.3 yards off the tee Thursday, which ranked sixth in the field when he finished his round. He was gaining nearly 2.5 strokes on the field after hitting nine of 14 fairways.

For 18 holes, at least, DeChambeau was not only hitting it far but also was hitting it straight, which isn't something he had always done in the past.

"That's been the most surprising part because I'm so used to hitting it everywhere," DeChambeau said. "Look, it could happen tomorrow. I don't think it will, but I feel really confident. Golf is a weird animal. You can never fully have it like Arnie (Arnold Palmer) said. You always think you have it one day, and then it just leaves the next. Just got to be careful."

The other parts of DeChambeau's game looked good in the first round too. He hit 15 of 18 greens and was gaining more than 2 strokes on the field in putting.

"Geez, he played great," said Keegan Bradley, who played with DeChambeau on Thursday and shot a 2-under 68. "It looked like Bryson to me. He hit the ball great, putted great, drove it really nice. It was good to see him. He was smashing drives again, and he played pretty much flawless golf."

Often called "The Scientist" because of his physics degree from Southern Methodist, DeChambeau said he might finally be done experimenting with his body and game.

"I want to be just stable now," he said. "I'm tired of changing, trying different things. Yeah, could I hit it a little further? Could I try and get a little stronger? Sure. But I'm not going to go full force. It was great. ... Shoot, I can hit my 8-iron 200 yards now. So it's an asset, and it was a fun experiment, but definitely want to play some good golf now."