The South African fired a superb 63 at Randpark Golf Club to lead the field of 240 players but he will be pushed all the way this weekend.
Both the Firethorn and Bushwillow courses will be used this week and Davidse started on the latter during his first round.
Recent weather conditions had softened the greens and Davidse took his chance to move one shot clear of Matthew Baldwin, Sebastian Heisele, James Morrison and South African trio Jared Harvey, Ockie Strydom and Erik van Rooyen.
He will start Friday's round on eight-under and his performance was made even more remarkable after he spent four days in hospital after last week's AfrAsia Bank Mauritius Open.
Davidse told the European Tour: "I'm obviously very happy. I've worked very hard. I went to Mauritius last week and didn't play too well. I was in hospital for about four days so I'm very chuffed today.
"I didn't really have any expectations coming into the week. I'm just out here to have fun, obviously, so I'm very blessed to be playing well."