Less than 48 hours after his Monday shock divorce filing from wife Erica became public, second-ranked McIlroy was set to start in the sixth group off the 10th tee at 8:25 a.m. (1225 GMT) alongside American Dustin Johnson and England's Justin Rose.
After a 10-minute fog delay, US club professional Michael Block struck the opening ball off the first tee to begin the showdown, in which McIlroy, top-ranked Masters winner Scottie Scheffler and defending champion Brooks Koepka top the list of favorites to lift the Wanamaker Trophy.
The focus and concentration so often shown in shotmaking by McIlroy was set for a supreme perseverance challenge after the four-time major winner from Northern Ireland's decision to end his seven-year marriage.
Asked on the eve of the tournament about his energy and how he was doing personally, McIlroy replied: "I'm ready to play this week."
He'll need to be if he is going to end a decade-long major win drought, although McIlroy's game enters on form after triumphs in his past two starts, a PGA Tour pairs event last month with Irishman Shane Lowry and last Sunday's fightback victory at the PGA Wells Fargo Championship.
"I think it's all about confidence and momentum and I have a lot of confidence and quite a bit of momentum coming into this week," McIlroy said. "It's just about trying to keep that going."
It is not the first time McIlroy has sought golf success after personal turmoil.
In 2014, he ended his engagement to Danish tennis star Caroline Wozniacki, then won the European Tour event at Wentworth four days later. McIlroy went on to win the British Open and PGA at Valhalla as well as a WGC tournament over the next three months.
'Difficult test'
Others hoping for an early charge off the 10th tee included five-time major winner Koepka, an American who is among 16 LIV Golf players in the field of 156. The tournament has 99 of the world's 100 top-ranked players.
Koepka will start two groups after McIlroy off the 10th tee alongside ninth-ranked countryman Max Homa, third at the Masters in his best major finish, and American Jordan Spieth, a three-time major winner who would complete a career Grand Slam with a victory at Valhalla.
Tiger Woods, a 15-time major champion and 2000 PGA Championship winner at Valhalla, and third-ranked Xander Schauffele, the reigning Olympic champion seeking his first major title, also have early starts on the back nine.
So does Sweden's Ludvig Aberg, who was runner-up at the Masters last month in his major debut.
Scheffler, a winner in four of his past five starts, was set for an afternoon start off the first tee alongside two other 2023 major champions from the United States -- US Open winner Wyndham Clark and British Open winner Brian Harman.
Other afternoon starters include two-time major winner Jon Rahm of Spain, who jumped from the PGA to LIV last December, and six-time major winner Phil Mickelson.
The 7,609-yard, par-71 layout features dense rough and damp conditions.
"With the greens probably being a little bit softer, we'll see how the course plays," Scheffler said. "The PGA especially has leaned into wanting to be a little bit more difficult test."
