Barnes and Piercy reached 13-under 200 on Grand National's Lake Course, and will be paired together again while jockeying for the lead Sunday.
''We were both hitting solid shots, giving ourselves good looks,'' Barnes said. ''And we both got off to a great start. We both holed about an 18- 20-footer on the first hole. So we saw balls going in the hole, saw good shots. Not so much competing, but kind of feeding off each other.''
Piercy birdied four of the first five holes. He has won twice on the PGA Tour.
''I've won a couple of times where I think a couple of the guys that are up there haven't won yet,'' Piercy. ''I think that's probably a bigger advantage is that I've gotten it done a couple of times. Not worried about locking up my card this week or stuff like that is another advantage.''
Barnes had birdies on Nos. 2 16 and 17. He's seeking his first PGA Tour win in 202 events.
Barnes came closest to victory with a runner-up finish in the 2009 U.S. Open. That also was the only other time he held or shared a 54-hole lead.
Second-round co-leaders Whee Kim and Mark Hensby were among five players a shot back. Both shot 68 in the event for players who failed to make the British Open field. Jason Gore had a 63, Will Wilcox a 65, and Emiliano Grillo a 67 to join the group at 12 under.
The 43-year-old Hensby, from Australia, surged with a 4-under performance over the final three holes, starting with an eagle on the par-5 16th.
He has limited tour status after battling rotator cuff problems in his right shoulder. Hensby won the 2004 John Deere Classic for his only PGA Tour title.
Gore knocked 10 strokes off his Friday score, when he had five bogeys for a 73. He rebounded with a bogey-free round and birdies on five of the final eight holes.
''Shockingly enough, I was still pretty positive,'' said Gore, whose only PGA Tour win came a decade ago. ''I knew I wasn't out of this golf tournament, I was only 5 back as bad as I played [Friday].''
Wilcox, a former UAB star from Birmingham, 6 under over the final nine holes, including an eagle on the par-5 16th.
''I putted really poorly on the front nine, and when I got to the back nine ... my putter kind of came alive,'' Wilcox said.