Sundowns reportedly paid R20-million to Portuguese outfit Vitória Guimarães to seal the deal just before deadline day.
Santos, who marked his arrival with a Man of the Match performance in the 4-1 win over Richards Bay, offered early signs of his quality as the champions returned to winning ways in the Betway Premiership.
Asked afterwards, Cardoso detailed the recruitment process that brought the Portuguese international to Tshwane.
"The quality of Santos was clear to us all, and his former club needed to release some players to make money.
"Nuno wanted a challenge abroad with different opportunities, and after our FIFA World Cup campaign, the Sundowns name seduced him."
The Sundowns coach indicated that getting Santos, as well as Miguel Reisinho, was not an easy step. He also pleaded for time.
Cardoso again pointed to the congested schedule as a stumbling block, forcing Sundowns to treat some fixtures as training sessions.
"The scheduling has an impact on our performances, but the quality of the game is also impacted.
"You rely on the quality, the emotion, and the commitment of the players when games arrive thick and fast."
The Downs mentor added that his biggest task this season, besides defending the league title, was to help rebuild the team.