Ronaldo struck the goal to lock up the scores at 2-2 before being substituted off ahead of the final moving to penalties.
Ruben Neves converted the winning penalty after Diogo Costa had saved from Spain captain Alvaro Morata.
Al Nassr striker Ronaldo was emotional during celebrations and later said: "A lot of joy. Firstly for this generation, it deserved a title. For the families, I had mine here... Winning for Portugal is very special. I've won a lot of titles, but there's nothing better than winning for Portugal. The tears and the fulfilment.
"It's beautiful. It's our nation. We're a small people, but we have great ambition. I've lived in many countries, played for many clubs, but when they mention Portugal it's a special feeling. Being captain of this generation is a source of pride.
"Winning a title is always the pinnacle for a national team. The future is short term. I had an injury and that was too much, too much... I pushed myself, because for the national team you have to push yourself."
Al Nassr? Yes!
On that injury, Ronaldo explained: "I'd already felt it in the warm-up, it had been there for a while. But for the national team, if I had to break my leg, I would. It's a title, I had to play and I gave it my all, I went as far as I could. I helped out with a goal."
Asked about under pressure coach Roberto Martínez, he said: "I'm very happy for him, for being a Spaniard, for having given his all for our country. It's a title we've already won, but this is our motivation, our hunger."
And on his club future, Ronaldo smiled: "Practically nothing will change. Al Nassr? Yes."