A Surprise Moriri brace and a late Katlego Mashego strike means the Brazilians advance 4-1 on aggregate, having drawn 1-1 in the island nation two weeks ago.
Sundowns put to bed any potential scares early on when Surprise Moriri netted from the spot in the seventh minute. The penalty was awarded after Mzikayise Mashaba was brought down in the area.
Ale Schut came close with a glancing header straight after the goal, while Mame Niang saw his shot shave the upright on 20 minutes.
Niang had another chance towards the end of the half which was saved as Downs went into the break with a 2-1 aggregate lead.
Themba Zwane forced an early save out of the visiting keeper after the break, but the second goal did come on 52 minutes - Moriri showing great composure to chip over the advancing goalie.
From there it was cruise mode for the Brazilians, with substitute Mashego twice threatening before adding the icing on the cake in the 88th minute after some good work from Anthony Laffor.
Sundowns: Mweene, Mphahlele, Mashaba, Mbekile, Schut (Nthethe 59), Kekana, T Zwane, Modise (Laffor 66), Mahachi, Moriri, Niang (Mashego 56)