Sabbatini rolled in a 14-foot birdie at the 18th hole to move to 14-under 196 heading into Sunday's final round.
Johnson shot an 8-under 62 and also birdied the 18th hole to vault from a tie for 22nd place into second place at 13-under 197.
Tim Wilkinson (63), Tim Herron (67) and second-round leader Chris Stroud (69) are three strokes behind Sabbatini in a tie for third place at 11-under 199. Seven more players were within five shots of Sabbatini's lead.
Sabbatini had two top-three finishes early this season but hasn't finished in contention most of the rest of year.