Crowd favourite Michael Block, the club professional who produced a feelgood story at last year's PGA Championship where he finished in a share of 15th place, hit the first shot of the major at the 484-yard par-four first hole as the fog lifted.
Defending champion Brooks Koepka, bidding to become the tournament's first repeat winner since he retained the title in 2019, is scheduled to start from the 10th tee at 08:47 ET (13:47 BST) alongside Jordan Spieth and Max Homa.
Five-times major winner Koepka, one of 16 LIV Golf players in the 156-player field, arrived at Valhalla fresh off a triumph in Singapore where he won his fourth title on the Saudi-backed circuit.
World number two Rory McIlroy, who has the second-best odds of winning the PGA Championship behind Scheffler, will go out two groups ahead of Koepka's threesome four days after earning his 26th win on the PGA Tour.
Tiger Woods, who has not played a PGA Championship since 2022 when he withdrew in pain after the third round, will be a further group ahead playing with Keegan Bradley and Australian Adam Scott.
For Woods, this will mark his first event since the Masters where the injury-ravaged golfer earned a tournament-record 24th consecutive made cut at Augusta National and finished last among those who played the weekend.
"My body's okay. It is what it is. I wish my game was a little bit sharper," Woods said this week.
New dad Scheffler will be bidding for a fifth win in his last six starts when he heads out from the first hole at 14:23 ET (19:23 BST) in the company of US Open champion Wyndham Clark and British Open champion Brian Harman.
World number one Scheffler, who sat out last week's tune-up event while awaiting the birth of his son Bennett, has had 24 days off since his last round of competitive golf.
This year marks the fourth time Valhalla has hosted the PGA Championship, and with greens and fairways softened by rain - and more scattered showers expected this week - the 7,609-yard layout should play long.
Players are being sent out in threesomes off the first and 10th tees for the opening two rounds before a 36-hole cut for the top 70 players and ties.
