Schwartzel fired a round of 8-under 63 that included a hole-in-one on the 12th hole in a round that had two stoppages because of thunderstorms.
McLardy carded a 69 and Drysdale had a 71 at the Royal Johannesburg and Kensington layout in Johannesburg.
Twenty-five players were separated by four shots at the top of the leader board.
The tournament is sanctioned by the European and South African tours.
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