Schwartzel had five birdies on each side in the second round to jump to 13-under after 36 holes. He's tied with Jamie Elson and Garth Mulroy, who each shot 7-under 64, for the lead.
Tyrone Mordt, who was tied for the first-round lead, had a 3-under 68 and is tied with Thomas Aiken (66) and James Kingston (62) for fourth at 12-under. Martin Maritz, the other first-round co-leader, shot 69 and is tied with Branden Grace (68) for seventh two strokes behind the leaders.
The Joburg Open splits the field between the East and West courses of the Royal Johannesburg and Kensington Golf Club for the first two rounds. All golfers play the East Course -- considered harder -- for the final two rounds.
Schwartzel took advantage of the West Course Friday, opening with back-to-back birdies, adding two more on Nos. 5 and 6 and making the turn at 5-under with a birdie at the ninth hole. After birdies at 10 and 12, Schwartzel closed with three birdies in his final four holes.
Elson and Mulroy played the East Course and each tore up the front nine. Elson birdied the last five holes of the first nine and Mulroy, after a bogey at No. 2, had four birdies and an eagle in making the turn at 5-under.