Doug Tewell is alone in second place at 7-under par, followed by Pat McDonald, Tom Jenkins, Rodger Davis, J.C. Snead and Vicente Fernandez, who share third place at minus-5.
Ahern wasted little time in breaking into red figures on Friday. He two-putted the first hole, a 530-yard par-5, for birdie but cashed in at the next par-5 hole.
At No. 6, Ahern knocked a 5-wood into a greenside bunker with his second shot but the 54-year-old holed out from 75 feet out of the trap.
'Someone was looking out for me,' said Ahern, referring to his unlikely eagle at the sixth.
Ahern cooled on the front side with three pars to close but he quickly returned to his birdie ways. He reached the putting surface in two at the next par-5, the 10th, and his 83-foot eagle putt left him with 16 feet for birdie. He rolled that putt home for birdie to reach 4-under par for the round.
Ahern continued his impressive form on the par-5 at 12. He two-putted for birdie from close to 20 feet, then birdied No. 13 to make it two in a row. Ahern drained a seven-foot birdie putt at the 15th to match Tewell at 7-under par, but Ahern had one more birdie left in his bag.
At the 18th, Ahern hit a 9-iron from 141 yards out to 30 feet. He sank the putt to take the first-round lead in a Champions Tour event for the second time this season.
'The putt on No. 18 was a good way to finish,' said Ahern, who also held a piece of the first-round lead at the Toshiba Senior Classic in March. 'It's just the first round and there is a lot of golf left to play.
'I made some nice putts today. If you're not making any putts out here, you're not going to score. If I could putt like that every day, I'd be a happy camper.'
Tewell started slowly with two birdies on his front side, but around the turn he went on a run of fabulous golf. He knocked a 3-iron onto the green at the par-5 10th and holed the 20-foot eagle putt.
At the 11th, Tewell sank a 15-foot birdie putt and one hole later he added an eight-foot birdie to get to 6-under par. Tewell ran home a 12-foot birdie putt at No. 16 to take the clubhouse lead with his 7-under-par 65.
'I really played well last week and felt I should have won,' said Tewell, who tied for third last week at the Columbus Southern Open. 'I just couldn't make some putts. The putter felt good in my hands today.'
Morris Hatalsky shot a 4-under 68 and made it through Friday's round without any bogeys, running his streak to 97 consecutive holes without a bogey. That matched the Champions Tour record set in 1994 by the late Jack Kiefer.
'The streak is a reflection of your overall game,' said Hatalsky, who won last week's Columbus Southern Open. 'My ball striking and short game have been good lately and I have a good rhythm going now.'
Hatalsky shares eighth place with eight other players including Hale Irwin, Bob Gilder and Jose Maria Canizares, whose son Alejandro, a freshman at Arizona State University, won the NCAA Men's Individual Golf Championship on Friday.
Gil Morgan, the 2002 champion, is part of a logjam at 3-under-par 69.