Keith Horne posted a 6-under 64 to climb into a tie for second place at 10-under-par 200. He is joined there by overnight leader Desvonde Botes, who shot a 69. Warrick Druian is one stoke further back at minus-nine.
McLardy came flying out of the gate with birdies at each of the first two holes. After a series of pars, the South African rolled off three consecutive birdies from the seventh to climb to minus-13.
He again notched back-to-back birdies from the 12th, but trouble was on the horizon. McLardy's birdie stretch ended with a bogey at the par-4 14th. He stumbled to another bogey at the 16th to fall back to 13 under.
'Bad stuff started going through my mind after 13,' said McLardy. 'You have to play one hole at a time but I kept on thinking ahead. It's tough to sometimes get some of that stuff out of your mind.
'But 13 under is okay. I got too involved with leaderboards and scores and trying to score mentally ahead of time is the worst thing you can do. You just have to hit it.'
Horne birdied the second and third before climbing to 7-under with a birdie on No. 7. He birdied both back-nine par-5s , Nos. 12 and 16. The South African capped his bogey-free round with a birdie at the last.
Botes stumbled to bogeys at the third and sixth. He responded with a birdie at the seventh and picked up another one at No. 10 to return to minus-nine. He then eagled the par-5 12th, but struggled to back-to-back bogeys from the 13th. He moved into a share of second place with a birdie at the 16th.
Gerry Coetzee fired a 7-under 63 to leap into a share of fifth place at 8-under-par 202. He is joined there by Marc Cayeux, Scott Dunlap and Titch Moore.
Andre Cruse, Bruce McDonald and Louis Oosthuizen each shot 2-under 68s to share ninth place with Sven Struver (69) at minus-seven.