Neither side was able to break the deadlock at Loftus but Cardoso insisted that keeping a clean sheet was half the battle won.
The two sides will resume hostilities at the Cairo International Stadium on Friday.
The Brazilians boss said on SABC after the game: "It's important to understand that not conceding is always very important in this kind of matches.
"Of course scoring is also very important. We got one objective, we didn't get the second one."
Sundowns only had one shot on on target, as Ahly had two goals ruled out for offsides, alongside hitting a post.
“I think first half was better than second one, we played more in trying to achieve it but I think that everybody understood that the positioning from Ahly on the pitch is very tough one, use four centre-backs, defending with a line of six most of the time, so very deep," the coach added.
"We tried different ways, we tried to find the spaces, we knew that it's going to be a match for two-three opportunities and we had to score out of them.
“We didn't [score], we are alive, we are struggling and I believe that we can finish the job over there in Cairo.”