Frost drained birdies on the 16th and 17th holes, finishing the day at 12-under-par 204.
That was one better than Fred Couples, who posted a 4-under 68 to move into second place at minus-11.
Falling into a share of third place at 10-under-par 206 was second-round leader Duffy Waldorf, who stumbled to a 1-under 71 Saturday.
Joining him there were 2010 Regions runner-up Michael Allen (69) and Morris Hatalsky (67).
Tom Lehman, seeking his third straight title at the event, completed a 3-under 69 to end in a five-player tie one shot farther back.
2014: NFL Cheerleaders [PHOTOS]
UPI Sports Results for September 19, 2014