Santos had strings of three consecutive birdies on each side at the East London Golf Club in building a two-stroke lead over four other players.
Santos was 1-under after four holes before running off three straight birdies to reach 4-under through seven. Birdies at Nos. 10 and 12 had Santos at 6-under and his second string of three birdies -- coming at Nos. 16-17 -- put him into the lead.
"I hit the ball solidly from the tee and my putting was all good," Santos said. "To shoot minus nine you have to play awesome golf, so I'm really pleased with every piece of my game.
"If the wind blows this is a very tough course but today if you put the ball in the fairway you had the chance to shoot a low round."