Australia's Peter Fowler (68) finished alone in third at 7-under 209 while fellow countryman Matthew Ecob had the low round of the day with a 6-under 66 to grab fourth at 5-under 211.
Coles began the day four strokes behind second-round leader Peter O'Malley and played the outward nine at even-par with a birdie and a bogey. It wasn't until the back half of the Kooyonga Golf Club that he made his charge up the leaderboard.
The 33-year-old fired off five birdies over the closing nine holes, including the birdie at the last that gave him the outright lead.
'Well, it's make or break this time, I'm pretty determined not to finish like I have in the past when I've been in contention,' said Coles. 'I'm just going to take it one shot at a time and focus on the first tee tomorrow.'
Molder, who battled Coles for the top spot, got off to a good start with four birdies on the front nine to make the turn at minus-seven. He added another birdie at the 13th to take the lead at 8-under.
The Georgia Tech grad made his only mistake of the day with a bogey at the 15th that moved him into a tie with Coles. He birdied the 16th to regain the lead at 8-under but Coles matched him moments later with a birdie of his own.
Molder, who turned pro in August of 2001, is playing in his first event as a member of the Buy.Com Tour. The 22-year-old rookie was the low amateur in the U.S. Open last year finishing in a tie for 30th and has been a member of two Walker Cup teams.
O'Malley, who enjoyed a commanding lead at the start of the round, struggled with six bogeys and two birdies to fall into a tie for fifth at 4-under 212. He was joined by Germany's Alex Cejka (70) and Gareth Paddison (70) of New Zealand, five shots off the lead.
A pair of Australians in Mark Hensby (70) and Andre Stolz (71) finished alongside New Zealand's Richard Lee (71) at 3-under 213.
Sweden's Richard S. Johnson (72), who earned his maiden European Tour victory at the ANZ Championship last month, finished one shot further back at 2-under 214. He was joined by Scott Laycock (69) of Australia and American Douglas Labelle (73).
Full field scores from the Jacob's Creek Open Championship