Sundowns were unable to see a way past Gallants after extra-time, and the game went to penalties where they lost in sudden death, 7-6.
Washington Arubi proved to be the hero with three penalty saves.
The loss is another blow for the Brazilians after their MTN8 run ended against Orlando Pirates in the semi-finals.
Cardoso has come under pressure from fans this season as a result of their inconsistent performances, although they currrently sit on top of the Betway Premiership standings after 10 games.
Speaking after the game, the head coach said in the Citizen: "The team is working with a big commitment and it was clear that today the players fought until the last minute.
"The players were all together and showed a lot of positive energy.
"That gives us a lot of good and positive things regarding the future. That is because when there's such a will to do things and commitment from the group, I think things will happen (improve) naturally."
Sundowns resume competitive duties when they face Remo Stars in the CAF Champions League Second preliminary round after the international break - where they will have eight players on duty for Bafana.
Marumo Gallants coach Alexandre Lafitte believes his side has what it takes to pull off another upset when they face Orlando Pirates in the Carling Knockout final at Peter Mokaba Stadium on December 6.
Golden Arrows coach Manqoba Mngqithi cut a frustrated figure after watching his side crash out of the Carling Knockout semi-finals despite dominating large spells against Marumo Gallants at King Goodwill Zwelithini Stadium on Sunday.
Orlando Pirates will enjoy home advantage when they take on Marumo Gallants in the 2025 Carling Knockout Cup final, after the Premier Soccer League (PSL) confirmed the venue and date for the much-anticipated clash.
Richards Bay mentor Ronnie Gabriel was proud of his players despite their 1-0 defeat to Orlando Pirates in the semi-finals of the Carling Knockout.
