Johnson's 18-under-par performance through three rounds has given him a two-stroke advantage over Mark Hensby and Todd Barranger, who carded a 10-under-par 62 on Saturday.
Johnson began the day with a four-shot lead, and continued to move forward with a pair of birdies at the 4th and 5th holes. Johnson added another birdie at the 10th, before dropping his first stroke of the day at the par-3 12th.
Johnson reclaimed a three-shot lead over Barranger, who was already in the clubhouse at 16-under, with a birdie at the 15th. However, he peaked the interest of his pursuers by bogeying the home hole.
Barranger's 62 is four stroke lower than his previous career-best on the BUY.COM TOUR. It also matches the lowest on the TOUR this season - set by Guy Boros in the second round of this event.
While Johnson is in search of his third career TOUR victory, Barranger is seeking his first. Not only has the 31-year-old Barranger not notched a win; he has yet to post a top-10 in 34 previous BUY.COM starts.
Saturday, Barranger birdied his final five holes to get into contention. He will be paired with Johnson in the final round. Hensby, winner of this year's Carolina Classic, will play alongside Gene Sauers. Sauers is tied with Brian Wilson for 4th place at 14-under.