Dana Quigley, who extended his Senior Tour record for consecutive events to 170, shares second place with Walter Hall at six-under par.
Lee Trevino, Dave Eichelberger, Gil Morgan, Jim Ahern, David Eger, last week's Senior PGA Champion Fuzzy Zoeller, Monday qualifier Morris Hatalsky and Miller Barber share fourth place at minus-five.
Sigel broke into red figures early Friday with a two-putt birdie at the par- five opening hole at Springhouse Golf Club. He added another birdie at four but climbed up the leaderboard with his play around the turn.
He holed a 15-foot birdie putt at the par-three eighth and made it two in a row when he drained a four-footer at nine. Sigel converted a six-foot birdie putt at 11 before reaching the green in two at the par-five 12th. He rolled in a 20-foot eagle at 12 and closed his round with a 15-footer at the last for a two-shot cushion.
'I probably only hit one shot I wasn't happy with,' said Sigel. 'I tried to stay below the hole. I putted the ball extremely well.'
Sigel has enjoyed a turnaround recently after operations on both shoulders. He did not post a top-15 finish until the Instinet Classic in May, but followed the next week with his seventh win on the elder circuit at the Farmers Charity Classic and continued with a tie for fifth the following week.
Quigley collected five birdies on his front side but ran into some trouble with his flat stick on the back. He missed a 15-foot par save at No. 11 and one from five feet at the par-three 14th.
'I hit a lot of shots close today,' said Quigley. 'I had four tap-ins out of eight birdies. You know you have to go low here. You know everyone else is going to go low.'
Hall also went low on his opening nine with five birdies but got setback by a bogey at No. 14. He posted back-to-back birdies at 16 and 17 to join Quigley and Sigel in Saturday's final group.
Barber bettered his age by four shots Friday with his five-under 67. He did not get things going until the back nine when he tallied five birdies.
'It makes you feel real good. My gosh almighty,' said the 71-year-old Barber. 'How many 71-year-olds can do it when you get right down to it? It's a great feeling. I had a nice time and had a lot of fun.'
Sammy Rachels, the 2001 champion, opened his title defense with a four-under 68 and is tied for 12th.
Full field scores from the BellSouth Sr. Classic