Craig Lile, one of four overnight co-leaders, is one shot back after his second round of 4-under 68. John Bele posted a 67 to move into third at 6-under-par 138 with South African Nic Henning one stroke further back at minus-five.
McLardy got off to a quick start as he birdied the par-5 second for the second day in a row. From there, he ran off eight straight pars before catching fire on the back nine at Leopard Creek.
The South African birdied No. 11 to get to 5 under. Like his round on Thursday, McLardy birdied the 13th through 15th. He climbed into the lead as he recorded a birdie at the par-4 17th. He parred the par-5 closing hole despite finding water off the tee.
'I'm trying to downplay all of that this week,' said McLardy, in reference to the winner being invited to the WGC-NEC Invitational. 'If you think about the rewards then it makes every shot harder. You don't need all those extra thoughts.'
Lile, who battled nausea and dehydration on the course, opened with an eagle at the second to climb to 6 under. He parred the remainder of holes on the front side before dropping a shot at the 10th.
He responded with birdies at the 13th and 15th before grabbing second with a birdie on the par-3 16th.
'Coming into this week, I felt as if I had something like a cold, which together with the heat made me feel awful,' said Lile. 'At the back of the eighth green I almost fainted and I felt like retiring. But I took some electrolytes after the ninth. From 15, a hole which he birdied, the electrolytes kicked in and I felt great.'
Simon Hurd and Desvonde Botes share fifth place at 4-under-par 140. Joachim Backstrom and Barry Painting are one stroke further back at minus-three.
Titch Moore and Keith Horne, who each held a share of the first-round lead, struggled to rounds of 2-over 74. They share ninth place at 2-under-par 142 with Louis Oosthuizen, Mark Mouland, Alan McLean, Thabang Simon, Andrew Butterfield and Ian Kennedy.
Fourteen-year-old amateur Ashleigh Simon, the first female amateur to play in a men's professional event in South Africa, struggled to a second round 79 and fell to 13-over-par 157. She leads three players -- Eugen Marugi (plus-14) and Steve Basson and Sammy Daniels, both of whom are tied for last at 15-over-par 159.
'I'm a bit frustrated at my finish. I made a few silly mistakes but tomorrow is another day,' said Simon.