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Yes Madrid dominated match but they could not create good goal chances. Without penalty they would face even more frustrating goalless draw as you said. This demonstrates typical difficulty at best teams to crack defensive opponent. You are also correct that single game does not give whole picture and therefore because of that true test for Real Madrid will be to determine whether or not they will be able to exhibit greater ability to create scoring opportunities in their future matches to convert their domination into goals.
Barcelona didn't actually put in a very good performance. Despite creating numerous chances, they couldn't score many goals against their opponent, who was shown a red card. Real Madrid is far worse off than them in a similar scenario. We've just started the league, and every team is playing matches that are likely to drop points. We saw an example of this from Atletico Madrid. I think this season will be a season dominated by Real Madrid and Barcelona. There's also a high probability that Real Madrid could drop points suddenly.