Byrd, seeking his fourth PGA TOUR victory, shared the lead with Kenny Perry, Ryan Palmer and two others when the second round began.
The course was drenched with over an inch of rain Thursday and, though no precipitation fell in the second round, overcast conditions kept the sun from drying off the fairways and greens and making the course play faster.
Perry and Palmer shot 69s to drop into a tie for second. Parker McLachlin, another first-round leader, shot a 70 to drop into a three-way tie for fourth with Charles Howell III (69) and David Toms (69) at 8 under.
Defending champion Zach Johnson (70) and Sugarloaf resident Stewart Cink (71) were seven strokes back at 5 under.
Byrd, who finished sixth in 2006 and tied for ninth in 07, was in the final group two years ago when Phil Mickelson finished the tournament a staggering 28 under.
Mickelsons penchant for attacking a course ripe for low scores impressed Byrd.
I watched him just kind of stay aggressive, stay aggressive, stay aggressive, and he kept making birdies, Byrd said. And I just kept telling myself that today. Its windy, but the greens are soft, so Ive got to keep trying to hit it close and keep trying to make birdies.
Byrd was upset with himself for a mental lapse that led to a three-putt at the par-5 sixth. It marked the only hole he played over par in the second round and just his second of the tournament.
You just cant give away shots in a PGA TOUR event with guys that are this good, Byrd said. And that was just a pure giveaway. You do that in junior golf. You dont do that on the PGA TOUR, but it happened and it might motivate me to play better.