Coetzee had a bogey-free round to get to 12-under 132 after 36 holes. Mark Tullo, with a 66, is tied for second at 11-under. Dawie van der Walt is also at 11-under but has four holes to finish in his second round. He's 7-under in his round.
Lightning caused two stoppages, with organizers calling off play about 4:30 p.m.
About one-third of the field has to finish second-round play Saturday before cuts and pairings are determined for the third round.
Peter Uihlein, with six birdies in his last 10 holes, is alone in fourth at 10-under and Romain Wattel, 7-under through 17 second-round holes, is in fifth at 9-under.
First-round leader Darren Fichardt was 1-under through 16 holes Friday and is tied with five players for sixth at 8-under.
Coetzee, looking for his first professional win, birdied Nos. 2 and 3 to get even with Fichardt and moved ahead with a birdie at the par-5 eighth hole. He posted back-to-back birdies at Nos. 12-13 and solidified the lead with birdies at 15 and 17.
Puzzle-maker slips 'Murdoch Is Evil' into Rupert Murdoch's Sunday Telegraph
Sign language interpreter at Mandela service called out as fake on Twitter