Springfield - Top-ranked defending champion Jason Day and British Open winner Henrik Stenson were chasing unheralded US leader Jimmy Walker after Sunday's third round of the PGA Championship at rain-soaked Baltusrol.
Walker, seeking a wire-to-wire victory and his first major title, fired a two-under par 68 thanks to four birdies on the back nine, the last a tap-in at the par-5 18th, to finish 54 holes at 11-under par 199 to pull one stroke ahead of Day.
"Just started feeling more comfortable with the golf swing," Walker said after two bogeys in the first five holes. "Just said 'Trust it,' on the swing and kept the pedal going. I feel good."
Day sank a stunning 74-foot birdie at the par-4 sixth, added a five-footer at the par-3 ninth and a tap-in birdie at 18 for a bogey-free 67.
"I played pretty good, gave myself some opportunities to shoot a low one but didn't really take them," Day said.
The fourth round had already started with the first groups only four holes behind the final third-round groups as the PGA of America kept the same pairings for the final round and played "lift, clean and place" rules near greens for the first time in tournament history in a bid to finish the year's last major on Sunday.
"It's exciting to be in this position," Day said. "I'm looking forward to the challenge of going out there and trying to win my second major.
"It would be nice to go back to back but I'm really trying to just put one foot in front of the other."
Day began the week fighting fatigue and illness, having never played Baltusrol's 7,428-yard layout until a practice round on the eve of the event.
"I played some really good golf," Day said. "To be honest I have no idea (how). It wasn't the greatest preparation, but once again the expectations came down and that kind of freed me up."
Stenson, who won his first major title two weeks ago at Royal Troon, fired his third consecutive 67 to share third on 201 with American Brooks Koepka.
"I was struggling with my long game today. It was a bit of a struggle for me to gather my rhythm. I just hope I can pick up some timing in my long game. I'll just keep the putting going and see where it takes us."
Koepka fired a bogey-free 66 to charge into the title chase.
"I played pretty well," Koepka said. "I drove the ball in the fairway. That's key. Every time I was in the rough I had a good lie. Those are the kind of breaks you need."
Koepka missed the British Open with a torn right ankle ligament that he rehabilitated until last week and wondered as late as Tuesday if he would play at Baltusrol.
"I've got it taped up. It feels pretty good right now," Koepka said. "The real test will be walking 36."
Sharing fifth on 203 were Japan's Hideki Matsuyama and Americans William McGirt and Robert Streb, who on Friday matched the record low major round with a 63.
Streb, who missed the cut at the year's first three majors, has not managed a top-10 finish in a US PGA event since his share of 10th at last year's PGA Championship -- 27 events of mounting frustration that could end with him hoisting the Wanamaker Trophy and taking a winner's prize of $1.8 million (1.6 million euros).