Coles completed 54 holes at 11-under-par 202. He has won three times previously on the Nationwide Tour: once in 2002, 2004 and 2006.
Chris Riley, who led after both of the first two rounds, managed a 1-under 70 in the third round and dropped into second place at 10-under-par 203.
B.J. Staten fired an 8-under 63 to move into third place at minus-9. He was followed by Andrew Dresser (66), Tom Byrum (65), Vance Veazey (67) and Matthew Every (67) at 8-under-par 205.
The round was delayed for one hour, 40 minutes due to the threat of thunderstorms.
Riley maintained his lead on the front nine as he opened with six consecutive pars. He dropped in a birdie on the seventh to move to 10 under.
The former U.S. Ryder Cupper parred five straight from the eighth and was caught on the lead at that point.
Coles made the turn at 8 under, after three birdies and a bogey on the front nine. He connected on back-to-back birdies from the 10th to grab a share of the lead at 10-under.
The Australian and Riley each bogeyed No. 13 to fall to minus-9, where they shared the lead with Staten and Greg Owen.
Riley moved back into the lead with a birdie on the par-4 14th. He parred out to end at 10-under.
'I didn't make any putts today. I'm actually pretty pleased with how I played,' stated Riley. 'I haven't been in this position in awhile. Playing in the last group is a lot different than playing in the middle of the pack.'
Coles parred three in a row after his bogey on 13. He birdied the 17th to match Riley in the lead, then birdied the last to take the overnight lead.
'I played really nicely today apart from two holes,' said Coles of his bogeys on nine and 13. 'The great scores this morning set the precedent for what I had to do this afternoon.'
The only other time Coles held the 54-hole lead was at the 2002 Jacob's Creek Open Championship, where he went on to win.
'I'm just trying to stand on the 10th tee tomorrow with a chance to win the golf tournament,' Coles admitted. 'That is what we all play this game for...to get in these situations and having the feeling of being in the hunt and having a chance to win the golf tournament.'
Owen carded two late bogeys to close out a 3-under 68. He was joined in a share of eighth place at 7-under-par 206 by Daniel Summerhays and Travis Perkins.