The event is being played on two courses - the East and West Courses of the Royal Johannesburg and Kensington Golf Club. The East course is playing to par 71, while the West is a par 72. The field of over 200 golfers will rotate courses on Friday before the low 70 and ties play the East course the final two rounds.
McLardy is trailed closely by fellow South Africans Warren Abery and Mark Murless, who each posted rounds of 8-under-par 64.
Marc Cayeux, Chris Gane, Vaughn Groenewald, Louis Oosthuizen, David Park and Brandon Pieters all shot seven-under-par 65 on the West Course. They were joined in a share of fourth place by Edoardo Molinari, who carded seven-under on the East course.
McLardy got off to a flying start and also closed with a bang. He dropped in back-to-back birdies from the first. McLardy quickly got to minus-three as he also birdied the fourth.
The South African gave that stroke back with a bogey at the fifth. He parred the next four, before flying up the leaderboard around the turn.
McLardy birdied No. 10 to move back to minus-three. He collected birdies at the 12th and 13th.
The 32-year-old eagled the par-five 15th to jump to minus-seven. McLardy's tee shot on the 15th came to rest behind a tree, but he hit a remarkable recovery shot to within three feet and drained the short putt for eagle.
McLardy also collected an eagle on the par-five 18th to end one clear of the field.
'I scrambled well on the front nine and was lucky to get away with everything that I attempted,' admitted McLardy. 'But I changed my rhythm on the back nine and things went a lot better. I was delighted with the two eagles to finish and with my back nine as a whole.'
Abery, like McLardy, played the West course in Thursday's opening round. Abery got going with birdies at the second and fourth. He made the turn in minus- three after a birdie at the ninth.
The 33-year-old came right back with a birdie on 10 then made five consecutive pars. Abery birdied the 16th and 17th before closing out his round in style with an eagle on the par-five closing hole.
Murless carded three birdies over the first six holes on the West course. After tripping to a bogey on seven, he turned in minus-four thanks to an eagle on the par-five ninth.
The 30-year-old posted a birdie on the 10th. Murless also closed with a solid string of golf. After a birdie on 15, Murless posted back-to-back birdies from 17 to end one behind McLardy.
Among those tied for 11th place are - David Dixon, Thomas Aiken, Ariel Canete, Gareth Davies, Jamie Little, Henrik Nystrom and Patrik Sjoland. They each shot six-under-par 66 on the West course, while Sven Struver and Hennie Otto carded six-under 65s on the East course.