Rickie Fowler fired an excellent opening 65 to set the clubhouse target on day one of the US PGA Championship at Bellerive Country Club.
The American finished second at the Masters Tournament earlier this year for this third top two finish in a Major Championship, as he continues his search for an elusive victory in one of golf's big four events.
Fowler came home in 31 to get to five under and open up a two-shot lead but he had an elite chasing pack behind him including 2015 champion Jason Day and Englishman Ian Poulter.
European Tour Member Pat Perez was also at three under alongside fellow Americans Stewart Cink, Austin Cook, Brian Gay and Ollie Schniederjans.
Fowler - playing in yellow in honour of Jarrod Lyle who passed away on Wednesday - birdied the 14th but gave the shot back on the 16th before bouncing back on the par five next to turn in 34.
A 15-footer on the first and an excellent tee-shot on the third had him in a share of the lead and he pulled away late in the round, holing a 30-footer from the fringe on the seventh before capitalising on the par five eighth.
Poulter had set the early pace as he sandwiched a stunning approach to the 12th with birdies from around 12 feet on the 11th and 15th but he dropped shots on the 17th and fourth to slip back.
Approaches to 12 feet on the seventh and eighth then moved the Ryder Cup hopeful back to three under.
Perez was bogey-free in his round, putting approaches inside eight feet on the 11th, 17th and eighth to edge his way up the leaderboard.
Australian Day has finished in the top ten in four of the last five years at this event and a nice approach led to a birdie on the 15th as he turned in 34.
Another birdie came on the first and while he dropped a shot after finding a bunker off the tee on the sixth, he birdied the seventh and eighth.
Cook birdied three of his last six holes to be the first man to set the target at three under, with both 2009 Open champion Cink and Schniederjans making four birdies and a bogey.
Gay recovered from bogeys on the second and fourth with six birdies in his 67.
Ross Fisher, Ryan Fox, Branden Grace, Billy Horschel, Yuta Ikeda, Mikko Korhonen, Hideki Matsuyama and Webb Simpson were at two under.
Defending champion Justin Thomas was three under after six holes but slipped back to a one under par 69, a shot clear of playing partners Rory McIlroy and Tiger Woods.