Ian Poulter had moved into a six shot halfway lead when the second round was finished this morning, but the 38 year old then struggled to a third round of 75 to end the day one shot behind Australian Ormsby, who shot a 68 to finish 12 under par as he seeks his first European Tour title on his 200th appearance.
Lee Westwood carded a 67 to finish alongside Ryder Cup team-mate Poulter and Germany's Marcel Siem on 11 under, Siem's 66 reviving his bid to prevent Rory McIlroy winning The Race to Dubai for the second time in three years.
Siem has to win in Turkey and at the season-ending DP World Tour Championship in Dubai to have any chance of overtaking World Number One McIlroy.
Ormsby's best finish this season is a tie for fifth in Morocco and the 34 year old from Adelaide admitted: "It feels great to be in this position. It's a great tournament, great field, so to be up around the front is great and to be leading it makes me pretty happy.
"My game is good. I'm hitting it strong, putting good. But I just walked off the ninth green and said to my caddie Richard that I've actually missed a few putts down the front nine. As good a score as I've shot, I still feel like I left a few out there. So I'll just keep trying to do what I'm doing and see how I end up."
Poulter blamed an "inexcusable" error as he failed to build on his advantage.
Seeking his first win for two years, Poulter completed a second round of 66 when the weather-affected event resumed on Saturday morning, taking his total for his last six rounds at the Montgomerie Maxx Royal to 33 under par.
"It's brought obviously a lot of players back into the fray," Poulter admitted. "Their dinner is going to taste lovely tonight and mine is going to taste horrible."
A three-putt bogey at the first was cancelled out by a birdie on the fourth, but Poulter then bogeyed the fifth and 11th before running up a double bogey on the 15th after his approach clattered into a tree short of the green.
"I'm most angry about the wedge shot which led to a double," the World Number 40 added. "That's inexcusable for me to make that error right there. A simple wedge shot puts me to 20 feet with an outside birdie look at worst, and I hit the tree, so I'm going to be angry about that for a little while tonight and then I'll be fine tomorrow.
"I'm going to get my head down and do the job tomorrow. Today was really disappointing to be out of rhythm after playing such great golf."
Westwood had been eight shots behind Poulter after the second round but was aided by holing his second shot to the seventh for an eagle as he charged up the leaderboard.
"It's been a while since I've been in contention, but generally when I get in contention, I know what to do," said Westwood, who won the Maybank Malaysian Open in April.
"I've been hitting the ball pretty solidly for a few weeks now. Just getting the odd break, holing the odd putt to keep the momentum going. I haven't really played the par fives well enough the first couple of days. Today I played them a bit better. All in all, I'm pleased with where my game's at. It's coming along nice."
Siem, Jamie Donaldson and Sergio Garcia began the week as the only men who could catch McIlroy in The Race to Dubai and although Garcia carded a superb 65 to move to five under, BMW Masters winner Siem has the best chance to keep the battle going to the final week.
"It's a little bit more interesting now for everybody and for sure I'll give it a shot tomorrow, try my best. That's what we are out here for, and there's why it's called Race to Dubai," Siem said.
"I'll have a good rest now and hope that my ball-striking is as good as today and the putter is hot. Can't wait to go."
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