Craig Parry carded a 6-under 65 and Jarrod Lyle posted a 5-under 66 to share second place at 13-under-par 200.
Ernie Els will have a very realistic chance to become the sixth player in golf history to win the same event four times in a row after a five-under 66 on Saturday. The No. 3 player in the world can join Tom Morris, Jr. (1868-70, 72 British Open), Walter Hagen (1924-27 PGA Championship), Gene Sarazen (1926, 28-30 Miami Open), Tiger Woods (2000-03 Bay Hill Invitational) and Hale Irwin (2000-03, 05 - Turtle Bay Championship five straight) if he visits the winner circle on Sunday.
The three-time major winner is tied for fourth with Brett Rumford, who also shot a 66 in the third round, at minus-11.
'I'd like to think that If I keep playing well, and stop shooting myself in the foot with some of my mistakes, I'll have a good shot at it Sunday,' said Els.
O'Hern, a left-handed Australian, flew out of the gate on Saturday with four birdies in his first six holes. He added another at the ninth to go out in 5-under 31.
O'Hern collected his sixth birdie of the round at the short, par-4 12th to get within two strokes of the lead. At the 14th, O'Hern's 35-foot birdie try circled around the hole before falling into the cup. He reached 13 under par with that birdie and trailed Lyle by a shot.
Lyle came back to O'Hern at the 14th when he missed an 8-footer for par. O'Hern took sole possession of the lead at the 17th with a 7-foot birdie putt.
Both O'Hern and Lyle parred out giving O'Hern the 54-hole lead. He will be in search of his first victory on the European Tour although the 2004 season was a breakthrough one for the Australian. He posted two runner-up finishes and came in 12th on the Order of Merit.
'Usually when you have a bit of a layoff, the short game goes, but I made some putts and never looked like making a bogey,' said O'Hern, who had arthroscopic knee surgery in the winter and played his first 18-hole round on Thursday.
Lyle eagled the second and was six-under on his round through 12 holes. He stumbled at the 14th, but the 23-year-old, who turned professional in 2004, is in position for his first victory.
Parry ascended up the leaderboard differently than his fellow leaders. He tallied three birdies on his front nine, but closed with three consecutive birdies to get his piece of second place.
Simon Dyson (65), Steve Webster (66), Henrik Stenson (68) and second-round co-leader Peter Lonard (70) share sixth place at 10-under-par 203.
Trevor Immelman managed a 1-under-par 70 on Saturday and is alone in 10th place at minus-9.
Colin Montgomerie shared the lead at the midway point with Lonard but four bogeys in his last six holes dropped him to a 1-over 72. He is tied for 11th with Camilo Villegas at 8-under-par 205.