The AmaZulu goal was scored by Dumisani Ngwenya while Lungisani Ndlela and Peter Ndlovu scored for Downs.
AmaZulu were the better side during the first half creating chances but were let down by poor finishing.
At the break Sundowns made two substitutions bringing on Ndlela and Fanyana Dhladhla replacing Jorge Acuna and Tyren Arendse. The game changed from then onwards with Sundowns stepping up a gear and dominating the second half.
The homeside took the lead in the 6th minute when Ngwenya scored with a shot from in front of the goal.
The Brazilians pulled a goal back in the 50th minute when Surprise Moriri crossed the ball for substitute Ndlela to score with a header.
Four minutes later Sundowns scored again through a corner by Lerato Chabangu which was headed down by Ndlela for Ndlovu to score with a close-range shot.
In the end Sundowns deserved the win.