The South African has another chance at a first European Tour title after his late run pushed him to 15 under and two shots ahead of Chile’s Felipe Aguilar heading to the final round at Leopard Creek Country Club.
Mulroy’s surge helped him overtake Jbe Kruger, who lost a four-shot advantage when he finished with a 1-over 73.
Mulroy had three birdies on the front nine, went bogey-free for the day and shot to the top of the leaderboard with five straight birdies from Nos. 13 through 17. He got a par on his last hole.
Mulroy twice has come close to getting a European Tour title on home soil, losing a playoff to Richard Sterne at the 2008 Joburg Open and then finishing second to Charl Schwartzel at the same tournament this year.
Kruger had four bogeys with three birdies to drop into a four-way tie for third as Mulroy and Aguilar passed him.
Aguilar was the closest challenger to Mulroy, getting seven birdies and four bogeys for a 4-under 68 to go to 13 under.