The wind greatly affected play and only five players in the field of 156 broke par for the round.
Van der Walt had five birdies and one bogey Thursday in taking a one-stroke advantage over Victor Riu, who closed his round with two birdies and an eagle at the par-5, 500-yard ninth hole.
Daniel Brooks, with an 8 at the par-5 14th but eagles at 7 (a 575-yard par 5) and 9, is in third at 2-under. Daniel Gaunt, who also eagled 7 and 9 but also had three bogeys in a row, is at 1-under. Also at 1-under, 70 is Olivier Rozner, whose round included back-to-back bogeys followed by three consecutive birdies.
Van del Walt, who has been a professional since 1996 but is yet to win a tournament, opened play Thursday on the second nine of the Aa St. Omer Golf Club with seven consecutive pars.
He made the turn at 2-under, however, after birdies at 17 and 18. He also birdied the second hole but suffered his only bogey of the day at the third hole. Birdies at 6 and 9 left him alone in the lead.