The 2011 U.S. Masters champion bagged an eagle and three birdies in a four-under-par 66 that earned a nine-under tally of 201, one ahead of compatriot Zander Lombard who carded the best round of the day with a scintillating 63.
Schwartzel dropped his first shot since Thursday after finding a bunker at the 18th, ending a run of 40 holes without a bogey.
Lombard found a purple patch of form when he struck five birdies and an eagle in seven holes from the sixth.
A further two shots back on six under is Joburg Open champion Haydn Porteous (68) who stayed in touch with the leaders despite a triple-bogey on the par-four seventh hole.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Level in a tie for third spot is overnight leader Anthony Michael (71).
The Pretoria Country Club has been a tough challenge this week and only 13 players are under par at the European Tour event.
(Reporting by Nick Said; Editing by Tony Jimenez; nick.said@thomsonreuters.com; +27832722948; Reuters Messaging: Reuters Messaging: nick.said.thomsonreuters.com@reuters.net)
