Winds in northern France that had affected play during Thursday's first round died down for Friday's play and scores improved significantly.
Dinwiddie, who was 1-over with five bogeys in the first round, was a case in point. He played bogey-free golf Friday to get to 4-under 138 for the tournament.
Van der Walt, who led after the first round, was even-par 71 in the second.
Dinwiddie, opening on the second nine at the Aa St. Omer Golf Club Friday, had three birdies over Nos. 14-17 to pull close to van der Walt. He added birdies at 5 and 8 for his 66.
Van der Walt had three birdies in his first six holes of the second round but posted four bogeys and one birdie in the final 10. Two of the bogeys -- at 10 and 17 -- came on holes he had birdies on Thursday.