Sundowns, who recently recruited Venezuelan forward Jose Ali Meza, Andile Jali and Toni Silva, beat the visitors from Botswana 3-0 in Phokeng outside Rustenburg on Saturday.
Sibusiso Vilakazi, Meza and Lucky Mohomi got the goals for the Brazilians, who used the game to prepare for their next CAF Champions League match with AS Togo-Port on July 17.
Downs drew their first two Group C contests against Wydad Casablanca and Horoya AC in the continental competition.
"We played a good opponent, Rollers, and this will help our preparation," Masandawana coach Mosimane told Rollers' official website.
"We have just come back for pre-season training and we had just five days of practice before this friendly. It showed, our tempo is a little bit low, but we will get there.
"We had to look at some of our new players, how we integrate them into the team. And we also had to look at our regulars from the previous season, and see their shape.
He added: "Rollers play quick balls, they are a confident team, they had a good chance in the first half and another good one in the second but they did not convert. We capitalised on a mistake by your goalkeeper to score the first goal.
"But such games are less about results and more about getting both teams into the right shape for later competitive matches."
The two sides will play another friendly in Gaborone this week.