Judas Moseamedi had given Maritzburg United the lead five minutes before the interval at the Moses Mabhida Stadium on Saturday evening.
But Sundowns striker Mauricio Affonso put his side 2-1 ahead with a second half brace, before the KwaZulu-Natal Capital City club were denied a late equaliser when Moseamedi’s 93rd minute header was ruled off-sides.
Maritzburg certainly played their part in an absorbing 90 minutes in Durban and in front of their sizable support base in the stands, coach Eric Tinkler's side were the more enterprising in the first half.
They were to make an early statement of their intent when with just a minute played, Moseamedi bustled his way through on goal, managing to force Sundowns keeper Denis Onyango into a mistake, but there was no end product as Daylon Claasen was unable to hit the target with the goal at his mercy.
United continued to trouble the Pretoria side with the intensity of their play, displaying some promising moments of inter-passing, although they weren't able to turn that into clearcut chances.
There was another opportunity in the 16th minute when Mxolisi Kunene flicked the ball to the back-post, but Dan Morgan flashed his header the wrong side of the upright.
Kunene then also fired a shot over the bar, but after that the Brazilians began to stamp their authority on proceedings.
They didn't overly threaten a well organised Maritzburg defence, but could have scored in the 37th minute when Affonso sent a header over the bar from just a few metres out, following a Gaston Sirino free kick.
With the Team of Choice getting numbers back to defend, Moseamedi was left up front by himself, yet he continued to trouble the Sundowns defence and after a storming run in the 38th minute, Onyango just about managed to keep out his parting shot.
Just two minutes later however and Moseamedi and his team-mates were celebrating after the big man chased down a goal kick form Richard Ofori, using his strength to get in between Onyango and Mosa Lebusa before toeing the ball into the net from a tight angle on the edge of the box.
After an evenly-balanced opening to the second half, United suffered a big disappointment in the 54th minute when Affonso stole into the box to glance in a header from Sirino’s searching cross as the Brazilians levelled matters.
Affonso sounded another warning when he headed wide 12 minutes later.
The Tshwane side continued to go the direct route and went in front in the 74th minute when Affonso glanced a header into the net following Sirino’s corner.
The Team of Choice refused to throw in the towel and came back looking for their second goal.
There were a couple of sharp chances for Kunene and Bandile Shandu. United then looked to have taken the match to extra time when Moseamedi snuck in at the near post to get on the end of Rushine De Reuck’s flick and head the ball into goal.
But their hopes were crushed as the off-side flag went up, Maritzburg’s brave run in the competition cruelly ended right at the final whistle.