Elias Ngwepe scored the only goal of the game just after halftime, with both teams finishing the match with 10 men.
There were rare starts for young Sundowns goalkeeper Jackson Mabokgwane and former Bafana Bafana striker Tyren Arendse as coach Trott Moloto shuffled his pack ahead of the Nedbank Cup Final against Mpumalanga Black Aces later in the month.
Arendse was instrumental in the first half, relishing his chance of first team football, and went close on a number of occasions.
Sundowns controlled the game in the opening period and might have been at least 3-0 up by the break, but had to make do with a 0-0 scoreline, as a mixture of poor finishing and good goalkeeping from Tapuwa Kapini kept them at bay.
But they made the breakthrough soon after halftime.
Stars failed to clear their lines in the 48th minute, and Ngwepe thundered home the loose ball from the edge of the area through a crowd of bodies to give Downs the lead.
And there was late drama as both teams were reduced to 10 men. First Arendse soured his comeback with a second bookable offence on 77 minutes to receive his marching orders.
But Stars could not take advantage of the numerical superiority as six minutes later they lost a man as well. Joseph Mkalipa, booked in the first period, made a crunching tackle on Robyn Johannes and deservedly was sent for an early shower as well.