The South African broke clear from a bunched leaderboard after firing a flawless seven-under 71 at Le Golf National, edging two clear of in-form Max Kieffer on a day of excellent scoring at the 2018 Ryder Cup venue.
Van Zyl picked up early shots at the third and fifth and then birdied nine, 10 and 11 for the second day running after knocking superb approaches to inside six feet on each hole around the turn.
Kieffer joined Van Zyl on eight under with a sparkling run of four birdies in six holes from the 12th, but Van Zyl responded with his sixth birdie of the round at 16 and he rolled in another at the last to close on 10 under par.
“Today was really a phenomenal round,” he said. “I felt really comfortable from tee to green and made a couple of nice putts. I’ve been in this position a couple of times and hopefully tomorrow we can pull through.
“I had surgery on both knees last year, which wasn’t great. You just don’t quite know what to expect coming out here but luckily I got off to a nice start at the beginning of the year and got the confidence building a little bit. I’m really looking forward to Sunday.???
Germany’s Kieffer, who has not missed a cut this year and has finished inside the top-30 in each of his last six starts with three top-10s, parred the last to cap a bogey-free 65 which was good enough for outright second place.
Bernd Wiesberger vaulted to seven under after he carded six birdies and just one dropped shot in a commendable 66, while Open de Espana champion James Morrison is a further stroke adrift after handing in a second consecutive 68, although he took the gloss off an excellent day’s work with his only bogey of the round at the last.
Two-time major champion Martin Kaymer also bogeyed the last after a wayward approach as he posted a third straight 69, and he shares fourth with Morrison and home favourite Victor Dubuisson after the Ryder Cup star recovered from a nervy start with three straight birdies from the ninth and parred in for a 69.
England’s Tyrrell Hatton reached seven under after his fourth birdie of the day at the 14th, but he dropped shots at 15 and 18 to slip to five under alongside American Brendan Steele, one of only three Americans in the field.
Veteran Mark Foster birdied the first three holes and got to seven under with his seventh birdie of the round at 16, but he was another to rue a poor finish after he missed the green at the 17th and then three-putted to run up a six, and he bogeyed the last in a 68 that promised to be much lower.
Foster is at four under along with Thongchai Jaidee, who surged up the leaderboard with a remarkable run of six consecutive birdies to start his third round, although the Thai ace played the last 12 holes in level par as he ended the day tied for ninth with Foster, Kristoffer Broberg, Daniel Brooks and Francesco Molinari.
But it was a frustrating day for overnight joint-leader Rafael Cabrera-Bello, who slipped seven shots off the pace after an error-strewn one-over 72.