The South African, on his Saint Omer debut, only dropped one shot as five birdies took him clear of local hope Victor Riu, whose birdie-birdie-eagle finish gave him a 68.
"I managed the ball really well today," Van der Walt, 38, said. "I have been doing that well the last few weeks but the putting hasn’t been great.
"I holed a few putts today which was good. I made a nice one on 17, from about 30 feet and downhill which broke about six feet, and another at 18 too but all credit to the greenkeepers because they slowed the greens down a little and if they didn’t do that there would be putts going off the green in that wind."
Both Van der Walt and Riu benefited from relatively early starts, as the winds grew heavier in the afternoon.
Like his South African rival, the Paris native has had a weak start to the season and is hoping this will put him in good stead heading into the summer.
"I want to try and keep the momentum going from that finish today and stay in a good state of mind and I think the weather will be nicer so it will be good," he said.
The most spectacular performance of the day was Daniel Brooks, who overcame a rotten start that saw him triple-bogey the 14th to slip to four over after five holes before knocking two birdies and two eagles to finish up on two under.
He lies third after his run, with fellow Englishman Simon Dyson one over.
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- Victor Riu