Springfield - Top-ranked defending champion Jason Day, battling illness and fatigue, birdied the par-4 11th hole Thursday at Baltusrol for a solid start to his repeat bid at the 98th PGA Championship.
The 28-year-old Australian, a seven-time winner in his past 18 starts, stood on one-under after three holes following a back-nine start alongside four-time major champion Rory McIlroy and five-time major winner Phil Mickelson.
McIlroy opened with three pars while Mickelson began bogey-par-par after finding a greenside bunker at 10 and missing a seven-foot par putt.
Sharing the early lead on two-under were Sweden's David Lingmerth, England's Paul Casey, Argentina's Emiliano Grillo and Americans Harris English, Jimmy Walker and Rickie Fowler.
Sunny skies greeted the early starters from the field of 156, the strongest lineup of talent in any event based on world rankings since their 1986 creation.
The 7,428-yard, par-70 layout features only two par-5 holes, those at 17 and 18 to ensure drama and eagle chances to the end in the quest for the top prize of $1.8 million (1.6 million euros).
Defending champion Day has struggled with illness and taken extra rest in the run-up to the year's final major tournament, playing only one practice round on the eve of the event at an unfamiliar course.
"I really don't look at it as a title defense," Day said after having taken his first major title last year at Whistling Straits. "I really look at it as I need to come back in, try and execute a game plan and try and win the tournament. I won it last year. That was fantastic and I need to focus on what I need to do this year to win the Wanamaker Trophy again."
McIlroy won the Irish Open and has nine other top-10 showings in US and European Tour events this year, including a share of fifth at the British Open two weeks ago.
"I feel like my game is in good shape," McIlroy said. "I can hit driver off the tee and from there, if I drive it well, I feel like I have a big advantage."
Mickelson won the 2005 PGA at Baltusrol and comes in off his 11th runner-up showing in a major, having lost a duel with Sweden's Henrik Stenson at the British Open.
At 46, the US left-hander would be the fourth-oldest major winner if he claims the title. And it doesn't hurt that "Lefty" is a fan favorite in the metro New York area.
"It not only makes it fun to play but it also keeps my energy level up throughout the round when I have a tendency to make a mistake or two," Mickelson said. "It helps me overcome some of those mistakes. I'm very appreciative for the way people here have treated me."
Stenson, US Open winner Dustin Johnson of the United States and Masters winner Danny Willett -- this year's major winners -- tee off in the afternoon feature group off the first tee, with only three final trios behind them.
Just in front of them are England's Justin Rose, American Patrick Reed and South African Louis Oosthuizen.
And the trio teeing off ahead of that offers two-time Masters champion Bubba Watson, another American in two-time major winner Jordan Spieth and Spain's Sergio Garcia, trying to win his first major title in his 73rd try and 70th consecutive major start dating to the 1999 British Open.
"If it doesn't happen, it's not going to change my life," Garcia said. "I'm not going to go in a cave and stay there until I die because I didn't win a major or anything like that. It's not that serious.
"I'm not going to lie. It would be nice to get at least one. But it's not the end of the world."