Rory McIlroy was hoping for a morning charge and set for an early test of his right foot issues as the 108th PGA Championship teed off on Thursday at Aronimink.
The 37-year-old is targeting a seventh major triumph after successfully defending his title at the Masters last month.
World No 2 McIlroy, however, has battled a nagging issue with his right pinky toe that forced him to cut short a practice round Tuesday after only three holes.
McIlroy had a blister under his toenail on his smallest right toe but after playing the back nine on Wednesday declared it was fine.
McIlroy has cushioned and separated the toe and switched to a half-size larger shoe with a wider toe area and softer leather.
That should ease any worries when he strides over the 7 394-yard, par-70 layout, teeing off at the 10th hole at 8:40am (12:40pm GMT) alongside American Jordan Spieth and Spain's Jon Rahm.
Spieth would complete a career Grand Slam with a victory this week, a feat McIlroy managed last year with his Masters victory.
Rahm could become the first Spaniard to win the event, the only major no Spanish player has ever captured.
Not since Spieth in 2015 has a player won back-to-back majors or the first two majors in a season.
Not since Jack Nicklaus in 1975 has a player captured the Masters and PGA Championship in the same year.
Other early starters include five-time major winner Brooks Koepka and fellow Americans Bryson DeChambeau and Xander Schauffele, both two-time major champions.
Top-ranked defending champion Scottie Scheffler starts off the first tee at 2:05 p.m. alongside England's Justin Rose, who won the 2013 US Open at nearby Merion, and Matt Fitzpatrick, the 2022 US Open winner who captured three PGA Tour titles in the past two months.
Scheffler has been a runner-up in his past three starts, including the Masters.
Fitzpatrick won the Valspar and Heritage crowns and alongside younger brother Alex captured the PGA Tour pairs event in New Orleans.
Alex Fitzpatrick won his first DP World title at March's Indian Open, then accepted US PGA Tour membership after his pairs victory and the past two weeks finished ninth at Doral and fourth at Quail Hollow.
Alex Fitzpatrick was also in the opening group to start Thursday at Aronimink, going off the first tee alongside Americans Ben Griffin and Braden Shattuck.
Another late-afternoon starter will be third-ranked American Cameron Young, who won The Players Championship in March and at Doral two weeks ago.