The 27-year-old forward had come under fire after failing to impress in Portugal's first two matches at Euro 2012, but he silenced his critics in the last two games - scoring three goals to power the Seleccao to the semi-finals in Poland and Ukraine.
Santos says he never doubted Ronaldo's quality and ranks the Real Madrid ace as the biggest talent on the planet.
"Cristiano Ronaldo is Cristiano Ronaldo," he told Globoesporte. "I do not know why people were so critical of him.
"Now they think he is the best player in the world? Of course he is."
Portugal will now lock horns with Spain in the last-four stage, and while the reigning European champions are viewed as favourites for the match, Santos thinks that Paulo Bento's side can progress.
"Portugal are doing what people expected," he noted. "They can win the Euros, they have a very dynamic squad.
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"Germany and Spain are still favourites, but Portugal are in the battle."
Greece were eliminated from the tournament on Friday following a 4-2 defeat against Germany, and Santos lamented that his side defended too deep.
"A defeat like this is not nice," the Portuguese coach added. "If I had been told we would score two goals and lose the match, I would not believe it.
"We missed Giorgos Karagounis. With him we would have had more possession of the ball and the chance to attack more.
"We never had the ball and when we had it, we were kicking it to the other side of the field. With that, we were not able to breathe and we were always under intense pressure."