The defending champions came into thew encounter on the back of a disappointing 1-1 with Kaizer Chiefs on Wednesday, which handed the advantage in the title race to Orlando Pirates.
The contest against Siwelele was effectively sealed in the first half when Masandawana raced into 5-1 lead.
Teboho Mokoena opened the scoring spree in the seventh minute before Tashreeq Matthews doubled the lead soon after.
Sundowns were 3-0 up after 21 minutes when Nyiko Mobbie put the ball into own net but the visitors pulled one back through Ghampani Lungu on the half hour mark.
The hosts though made sure they would go into the halftime break with a significant advantage with Matthews completing his brace and Brayan Leon bagged a goal.
Lungu then netted his second just after the interval to make the score 5-2 but Sundowns once again pulled away when Leon completed his hat-trick.
Siwelele scored another two goals towards the end to bring some respectability to the scoreline but it was Sundowns that took all three points.