They rested a few of their key players in captain Hlompho Kekana, Khama Billiat and Denis Onyango, with the likes of Aubrey Ngoma handed a first full start.
The match started in swift fashion, where Downs nearly took a first minute lead through Jeremy Brockie, while the hosts responded after Ruzaigh Gamildien found his shot blocked.
Following the 10th minute spell, Percy Tau whipped in a free-kick from outside the box that sailed straight into the hands of Ludiwe Mpakumpaku.
Then in a rare attacking foray, All Stars through Mtshuleko Ndlovu had a crack at goal, but it was more half-hearted than a heart in the moment scenario as it went way over the bar.
The youngster took another swipe at goal, but was unfortunate to see his effort deflected away for a corner by Motjeka Madisha.
All Stars continued piling the pressure early on in the second half, and Lucky Setelele missed a golden opportunity after miscuing in front of goal.
The Brazilians were given another scare later on when Ndlovu capitalised on poor defending, but he failed to make Wayne Arendse pay with a wayward shot.
They were made to pay and it was indeed Tau who made them pay after he got on the end of Themba Zwane’s through ball to beat Mpakumpaku with a cool finish in the 60th minute.
The Bafana Bafana international looked for his brace, and after finding acres of space inside the box following Gaston Sirino’s supply, he failed to double his tally.
Tau failed to finish yet another move, with the goal at his mercy when he blasted way off goal following Thokozani Sekotlong’s layoff.
Sirino followed suit after racing through on goal, he was denied by the outstretched leg of Mpakumpaku to secure his first goal, as the four-time champions march into the next round.
All Stars: Mpakumpaku, Ndiki, Makua, Gertse, Williams, Mbunjana, Gamildien, Ndlovu, Tshabalala, Mvalo, Setelele.
Subs: Goldman, Abrahams, Mogotlane, Matlou, Mrawu, Jackson, Abrahams.
Sundowns: Brimah, Zulu, Morena, Arendse, Madisha,Manyisa, Ngoma, Mabunda, Zwane, Brockie, Tau.
Subs: Mweene, Vilakazi, Langerman, Ngcongca, Sekotlong, Sirino, Lebese.