Cardoso made wholesale changes to the starting eleven, retaining only midfielder Nuno Santos from the squad that had beaten Orlando Pirates 2-1 just days earlier.
While he had anticipated some rotation, the number of changes ultimately left his side vulnerable to Galaxy's high press.
"The team that started today had the ability to win the match, but unfortunately, we shot ourselves in the foot, two shots and one in each foot," Cardoso explained. He emphasised that the quality was there, but mistakes at critical moments proved decisive.
Divine Lunga's loss of possession led to the opening goal, while Thato Sibiya conceded a penalty, giving Galaxy an early advantage.
"When you don't convert the chances you had and you let yourself make mistakes, you're down 2-0 in a match that is played in conditions that are difficult to cope with," the Portuguese tactician said.
Cardoso stressed that the defeat was not solely down to rotation, but a combination of errors, missed chances, and Galaxy's ability to exploit Sundowns' temporary disorganisation.
Looking ahead, he wants to shift focus to the league, where Sundowns face a crucial clash against AmaZulu at Moses Mabhida Stadium on Tuesday.
"We have the quality to win matches, and we should not wait until we are out of a competition to do well in others," he said.
