IRVING, Texas, May 19, 2012 (AFP) - Dufner completed 54 holes on eight-under par 202 at the $6.5 million event, one stroke ahead of compatriots J.J. Henry and Dicky Pride and Australian Day with Fiji's Singh on 204 and Aussie Marc Leishman and Swede Jonas Blixt on 205.
Dufner had a bogey at the par-4 third, answered with a 10-foot birdie putt at the par-4 sixth and a 14-foot birdie putt at the par-4 14th to lead as he had after 36 holes on a day where nine players led or shared the lead.
"It was a stress-free round for me," Dufner said. "I was in position a lot off the tee, which enabled me to be aggressive with iron shots and didn't have too many must-make par putts."
Dufner defeated Ernie Els in a playoff three weeks ago to win at New Orleans for his first career PGA title in 163 attempts, snapping a career win drought that including squandering a late lead at last year's PGA Championship.
"It was a tough thing for me to get over that hurdle," Dufner said. "I'll have those thoughts in the back of my mind and encourage myself to think about those things and try and close this out."
Day opened the front nine and back nine with birdies and also birdied the two par-5s, the seventh and 16th holes. But a bogey at 18 after missing a short putt kept him from matching Dufner atop the leaderboard, settling for a 67.
"I played great," Day said. "It was tough conditions out there today with the wind, but I felt like I was trying to stay as patient as possible. Got away with a few shots out there, but overall very happy with how the day went."
Day, who won the 2010 Nelson at TPC Four Seasons, expects a shootout for the crown on Sunday.
"Tomorrow is going to be tough," Day said. "There are a lot of extremely outstanding golfers up there on top of the leaderboard. I just have to stay disciplined within myself.
"The guy that obviously makes the least amount of mistakes out there is going to win. That's just how things are going to go. So I feel like I'm in a good spot."
Singh, 49, fired a 66 to stand two strokes back, a bogey at 18 dropping him back after an eagle at the 16th and a birdie at the 17th as he bids for his first PGA title since the 2008 Deutsche Bank Championship.
"I haven't been in this position for a while," Singh said. "I've been looking forward to this. I've worked really hard, I haven't stopped working. My game has been coming around, but there wasn't any sign of scoring and this is the first day where I kind of went out there and scored well."
Leading scores on Saturday after the third round of the $6.5 million PGA Tour Byron Nelson Championship (USA unless noted, par 70):
202 - Jason Dufner 67-66-69
203 - J.J. Henry 68-68-67, Jason Day (AUS) 68-68-67, Dicky Pride 66-68-69
204 - Vijay Singh (FIJ) 68-70-66
205 - Jonas Blixt (SWE) 68-70-67, Marc Leishman (AUS) 65-69-71
206 - Rich Beem 68-70-68, Bob Estes 73-68-65, Joe Durant 70-71-65, Scott Piercy 66-70-70, Keegan Bradley 67-68, Matt Kuchar 66-68-72, Ryan Palmer 64-70-72, Pat Perez 67-67-72
207 - Jason Bohn 70-70-67, Jimmy Walker 70-68-69, Andres Gonzales 66-72-69, Padraig Harrington (IRL) 68-69-70, Chad Campbell 68-66-73
208 - Phil Mickelson 70-69-69, Shane Bertsch 70-70-68, Graham DeLaet (CAN) 71-68-69, James Driscoll 67-71-70, Greg Owen (GBR) 67-71-70, Billy Mayfair 69-68-71, Ken Duke 69-67-72