VERSAILLES, 4 Jul 2015 (AFP) - The 36-year-old van Zyl was one of nine players parked on five under par halfway through his round before a triple-birdie burst around the turn propelled him into the lead.
He held onto that with a run of pars down the back nine before birdies at 16 and 18, where he hit a superb approach over the water to three feet, gave him the outright lead at 10 under.
Two shots further back was Germany's Maximilian Kieffer, who signed for a 65, with Bernd Wiesberger of Austria alone on seven under thanks to a 66.
French number one Victor Dubuisson (69) and former world number one Martin Kaymer of Germany (69) were both four shots off the lead, level with James Morrison of England (68).
"I just felt really comfortable out there today," said van Zyl, who has remained during his career very much in the shaodow of such major title winning countrymen as Ernie Els, Trevor Immelman, Louis Oosthuizen and Charl Schwartzel.
"Felt good out there yesterday, as well. Finished in an ambulance. But other than that, I played nicely tee‑to‑green. I hit it really good. I think I missed one fairway, hit 18 out of 18 greens. Made a couple of putts when I needed to."
Winless on the European Tour despite a couple of runner-up finishes, van Zyl has under his belt 13 wins in the second-tier Sunshine Tour back home and he believes that could help him on Sunday.
"I think it will play a big role. End of the day, it's the same situation. Stage is a lot bigger. I've been in this position a couple of times. Hopefully tomorrow we can pull through."
The fast-emerging 25-year-old Kieffer has made the cut in all 17 tournaments he has played in this year, although he is still chasing his first win.
"I feel like I'm good enough to win," he said. "I think I learned enough in the last two tournaments where I was in the final round to win.
"But we will see. I don't know if it's the time. I just have to hit good golf shots tomorrow and then we will see."
Dubuisson, who is looking at 25 to become the first home winner of the French Open since Thomas Levet in 2011 said that his chances were alive, but all would depend on how he starts on Sunday.
"I think tomorrow I will need a very good start if I want to have a chance," he said.
"I think you need to be like one-, two-, three-‑under after six, seven (holes), to really get a chance. Because when you start the back nine, from 12 to 18, it's really difficult to make birdies.
Most of the fireworks early in a day when the temperatures again soared into the mid-30s came from Thai veteran Thongchai Jaidee.
Having just made the halfway cut by two strokes after rounds of 70 and 74, Thongchai needed a big early effort to get back in contention and that he did by birdieing the first six holes.
That shot him up the leaderboard to four under for the tournament through 14 holes, matching the overnight leading mark.
Thongchai, who has won six times on the European tour, came close to winning the French Open last year before Graeme McDowell triumphed.
McDowell, who was aiming to make it three French Open titles in a row this week, failed to make the cut on Friday as did former world number one Lee Westwood.
Leading third round scores in the French Open at the par-71 Golf National on Saturday:
203- Jaco Van Zyl (RSA) 68-71-64
205 - Maximilian Kieffer (GER) 70-70-65
206 - Bernd Wiesberger (AUT) 68-72-66
207 - Victor Dubuisson (FRA) 68-70-69, Martin Kaymer (GER) 69-69-69, James Morrison (ENG) 71-68-68
208 - Tyrrell Hatton (ENG) 71-68-69, Brendan Steele (USA) 72-69-67
209 - Francesco Molinari (ITA) 70-69-70, Daniel Brooks (ENG) 73-66-70, Kristoffer Broberg (SWE) 72-69-68, Mark Foster (ENG) 70-71-68, Thongchai Jaidee (THA) 70-74-65
210 - Andy Sullivan (ENG) 71-70-69, Jake Roos (RSA) 73-71-66, Rafael Cabrera Bello (ESP) 68-70-72, Trevor Fisher Jnr (RSA) 74-71-65
211 - Peter Hanson (SWE) 72-71-68, Mikko Korhonen (FIN) 70-71-70, Gary Stal (FRA) 73-69-69
212 - Andrew Johnston (ENG) 73-71-68, Jason Scrivener (AUS) 75-69-68, Richard Bland (ENG) 76-70-66, Michael Lorenzo-Vera (FRA) 75-70-67, Jerome Lando-Casanova (FRA) 74-70-68, Marcus Fraser (AUS) 73-69-70