Stiles stands at 14-under-par 196 through three rounds, one shot off the 54-hole tournament record of 195 set by Mark Hensby in 1998.
Michael Putnam shot a 5-under 65 to join overnight co-leader Jay Delsing in second place at 10-under-par 200.
Delsing, competing just one week after the death of his father, shared the second-round lead with Stiles but managed just a 2-under 68 on Saturday.
Joel Edwards and Deane Pappas shot matching, 3-under 67s and share fourth place at 9 under.
Tommy Tolles fired the round of the day at Hardscrabble Country Club -- a 7-under 63 -- to vault from a tie for 35th place overnight into a share of sixth. He was joined at minus-8 by Cliff Kresge (65), Johnson Wagner (66) and Scott Gutschewski (67).
Playing with Delsing and Pappas in the final threesome off the first tee, Stiles collected two birdies and seven pars in a steady front nine, making the turn at 10 under.
But the 32-year-old, three-time champion didn't start pulling away until his final nine holes.
After his birdie at the ninth, Stiles picked up three more over the next three holes to assume the lead.
'I know what's going on out there, but I wouldn't say I watch leaderboards,' Stiles admitted. 'I don't watch them on every hole, but I'm usually pretty aware of what's going on around me.'
Stiles dropped his only shot with a bogey at the par-4 13th, then picked up two strokes with birdies at 14 and 18.
Stiles' lead actually doubled from two shots to four shots with his birdie at the par-4 18th, this after Delsing was unable to get up-and-down for par.
'I feel a lot better at four shots than I would at two,' said Stiles. 'Obviously I've got more shots to play with, but I know the guys behind me are playing well and anybody can come out from the back of the pack.'
Stiles holds the 54-hole lead for the fifth time on the Nationwide Tour. He won twice in his four previous times in this position, and has three victories overall.
'[This is] definitely the best I've hit the ball in a while,' Stiles claimed. 'I get in those runs where I start hitting the ball well and if I can get the putts to start dropping, then my confidence goes up. When my confidence goes up, that's the big thing.'