Nyasha Mushekwi got the goal for Sundowns, sending them up to second place on the Premiership log, just two points behind new log leaders Ajax Cape Town.
Sundowns should have claimed a more comprehensive win over Vasco due to the number of scoring chances they created in the first half, but in the end they scored from what was - unbelievably - their only shot on target.
Both sides fielded reshuffled defences, Sundowns playing youngster Siyabonga Ngubane out of position at right-back (though he acquitted himself more than adequately), while Vasco gave Vincent Julius his first start of the season in central defence.
The visitors started confidently, but from the moment Sundowns created their first scoring chance, in the seventh minute - from which Nyasha Mushekwi inexplicably failed to get away a shot before teeing up Katlego Mphela to blaze wide - it was virtually one-way traffic.
Mushekwi made up for his earlier hesitancy in the 18th minute when the put the Brazilians ahead. The striker ran onto a perfectly-weighted pass from the excellent Elias Pelembe and beat Jason Barnard with a low shot into the bottom corner of the net.
The Zimbabwean should have had a hat-trick in the first half, as he squandered a good opportunity straight after his goal and then glanced a header wide of the target in the 35th minute from another terrific cross by Pelembe.
While Vasco occasionally threatened through Sibusiso Zuma and captain Keenin Lesch, they were unable to really test goalkeeper Wayne Sandilands, who was not called upon to make any notable saves in the first 45 minutes.
The second half was a frustrating one for the Brazilians. They were unable to get going in attack and, as the half wore on, Vasco grew in confidence and began to threaten an equalising goal, particularly late on when they won a number of corner-kicks.
However, Sundowns’ somewhat makeshift defence did an excellent job in protecting their lead and the Cape side were able to create only one genuine chance: Armogam sprinted free on a counter attack in the 77th minute but put his effort over the crossbar with Esrom Nyandoro putting him under pressure.