As the sun came out and the winds died down in benign afternoon conditions, Van der Walt and Englishman Daniel Brooks both looked to be storming clear of the field but came sliding back down on the back nine.
Van der Walt had three bogeys on the way home for a two over back nine and a level par round of 71, which meant a share of the lead on four-under-par.
The Texas resident was disappointed with his finish, after carding three birdies in an impressive front nine to move three clear of Dinwiddie temporarily, but was happy to still be in a great position to claim a first European Tour title at the end of it all.
“I played really solid the first few holes and it seemed no matter where I was on the green I made putts,” said the 38 year old. “I bogeyed the par five ninth though with a six iron in my hand and that took the momentum out of my round a little.
“I didn’t hit bad shots but my chipping around the greens was not great and all my bogeys were from next to the green. I'm disappointed but I'm still in there and I was shocked walking up 18 to see I was still top.
“I'm still optimistic for the weekend, if I can keep striking the ball well and get my wedge to work a bit better who knows what can happen.”
Justin Walters also put in a good showing ahead of the weekend, joining a share of sixth on two-under-par. He had to dig deep heading into the week after his first round began with a double, but the two-time Sunshine Tour champion was up to the task and shot a Friday 69 to burst into contention.