By shooting the round's second-lowest score, the Englishman jumped from a tie for sixth place when the day began to a one-stroke lead over second-round leader and native South African James Kingston (71) for a total of 3-under 213 through 54 holes.
Wilson's total is 4-under 212.
His bogey-free round included birdies at the first five holes.
A par at the last helped him maintain his position as the leader heading into Sunday's fourth and final round.
Kingston's round of 1-under 71 included three bogeys and a double-bogey at No. 17 which cost him a share of the top spot.
South African Garth Mulroy moved into third place with an 8-under 64 for a total of 2-under 214.
He opened with an 8-over 80 Thursday and was tied for 34th when Saturday's round began.