Van Rooyen birdied the last three holes at Royal Golf Dar Es Salam to cap a five-under 68 and vault into the outright lead on eight under par, one ahead of Jorge Campillo and two clear of Sean Crocker.
The South African is well placed to finally claim his maiden European Tour title after near-misses in his homeland and in Ireland last year, while he was also runner-up at last month’s Qatar Masters – one of his two top-10 finishes in March.
Van Rooyen was one of only three players to break 70 in Friday’s windswept second round, and he produced a spirited recovery from an early dropped shot at the second as he birdied the seventh and ninth.
The 29-year-old picked up further shots at 12 and 13 before giving one back at the next, but his grandstand finish lifted him to the top of the leaderboard and he is hopeful of banishing the memories of his disappointing final-day 74 at last season’s Irish Open having slept on the 54-hole lead.
“I was quite nervous last year and I think I’ve been in this position a bunch of times now,” he said. “The nerves will be there again, but I love to be in this position. What we’ve been doing up until now has been great, so we’ll just keep doing that.
“I struggled with my rhythm and my tempo in the beginning today, but I think I just kind of found my flow on the back nine. I didn’t actually realise I made five birdies coming in!”
Van Rooyen’s playing partner in Sunday’s final group will be Campillo, who made five birdies and just one bogey in a solid 69 that earned the Spaniard outright second ahead of Crocker, who was tied for the lead until he found water at the 16th and ran up a double-bogey six.
Crocker did manage to hit back with a birdie at 17, but he missed another good chance from eight feet at the last as he settled for a 72 and third place on six under par.
Scotland’s Grant Forrest climbed 12 places up the leaderboard despite an erratic start to his third round in which he carded three bogeys and a pair of birdies before making his first par of the day at the sixth.
Further birdies at eight and nine got Forrest back on track and he cruised home in 34 with three more gains as he signed for a 69 which left him level with Wade Ormsby, Julian Suri and Lee Slattery on five under.
Slattery offset five birdies with four bogeys in a battling 72, while first-round leader Jordan Smith slipped six off the pace with three consecutive bogeys from the 14th before he hauled himself back into contention with the fourth eagle-two of the day at the penultimate hole.