Springfield - Jimmy Walker, who missed the cut in three of his past four major starts, fired a five-under par 65 Thursday to grab a one-shot lead in the first round of the PGA Championship.
The 37-year-old American, whose best major showing in 17 starts was a share of seventh at the 2014 PGA, owned a one-stroke lead over Argentina's Emiliano Grillo on a day when stars Rory McIlroy and Phil Mickelson struggled at par-70 Baltusrol.
"All in all it was a great day," Walker said. "I feel like I've prepared and I'm ready to go this week. It's nice that's what showed. I felt like I was ready to go. Winning a major is huge. Three more days to go."
Two strokes adrift were England's Andy Sullivan and Americans James Hahn and Harris English.
"It's a good start but there's a long way to go," Sullivan said.
Walker, a back-nine starter, followed his lone bogey at the sixth with a 31-foot birdie putt at the seventh to grab the lead. Two closing pars kept him there and had him pondering possibilities in a year that has already produced three first-time major winners.
"I don't think it's coincidence or anything," Walker said. "They are all good players and it was just a matter of time. So just keep that rolling."
Walker opened with birdies at the 13th and 15th holes, a 10-foot birdie putt at 16 and back-to-back birdies at the par-5 18th and par-4 first, the latter on a 20-foot putt.
Unheralded players topped the leaderboard while big names stumbled as four-time major winner Rory McIlroy, ranked fourth, fired a birdie-free 74.
Five-time major winner Phil Mickelson, a 10th-tee starter fresh off a British Open runner-up effort, made four bogeys in his first 11 holes but charged in with three birdies for a 71.
"I'm proud of the way I hung in there and fought and got three back coming in," Mickelson said. "If I can shoot in the 60s tomorrow I can get back in it.
"To make a bogey on 18, the only real birdie hole, I threw away a lot of shots. It's not the start I wanted. It's not indicative of the way I'm playing."
Defending champion and world number one Jason Day of Australia shot 68 to hang three off the pace despite fighting fatigue and illness and playing only one practice round. He had the best spot of any major winner on the leaderboard.
"Drove it nicely. Played pretty well. Missed a lot of opportunities. I haven't had the greatest putting display," Day said.
"I'm pretty pleased. I hit a lot of quality shots. To hit it where I wanted and execute like I did, really positive going into the next three days."
Grillo made a 30-foot birdie putt at the the par-3 fourth and added a 12-foot birdie putt at the fifth. After finding a greenside bunker and making bogey at seven he birdied the eighth and ninth and followed another bogey at 10 with birdies at 14 and 15.
"It's very tricky out there," Grillo said. "If you miss the greens in the wrong spot, you're going to have trouble getting up and down. It's a very hard course.
"I just keep it pretty simple -- worry about your own ball and not so much what everybody else is doing."
Grillo was inspired by the Masters and US Open wins of countryman Angel Cabrera.
"He won two majors when I was a kid," Grillo said. "Watching him wear the green jacket back in Argentina, it was a lot of motivation."
British Open winner Henrik Stenson of Sweden, US Open winner Dustin Johnson of the United States and Masters winner Danny Willett -- this year's major winners -- were off in the afternoon. Stenson birdied the second hole while the others were level through two.