Mikel Merino's stoppage-time strike gave Spain a 1-0 win in Dallas and ended Ronaldo's career-long pursuit of a global title, while also bringing to an end Roberto Martinez's tenure as Portugal head coach.
Ronaldo made the 223rd appearance of a Portugal career that has so far lasted 23 years and, although he confirmed he would not go back on his decision that this would be his final World Cup, he is not yet ready to say whether it was his international swansong.
Speaking to reporters after the match, the 41-year-old said: "I am sad to leave like this but I have given everything, always given my best. I go with a clear conscience. This is football, it is the life of a footballer. Sometimes you win, sometimes you lose. You have to carry on.
"It was my last World Cup, yes, but as far as the rest of it is concerned - there will be time to think, to be with my family; not make decisions in the heat of the moment."
Ronaldo helped Portugal win Euro 2016 and has twice lifted the Nations League with his country.
"I will wake up tomorrow the same way I woke up today - with a clear conscience," he added.
"I gave my all. I won three titles with Portugal. Before Cristiano, Portugal had never won a big trophy.
"The best trophy I won with the national team was 2016, which for me has the same dimension as the World Cup. So I repeat - I leave here with a clear conscience. Tomorrow will be another day and life goes on."
Ronaldo's role – and his continuing value to Portugal – was a matter of much debate during the tournament, with Martinez criticised for repeatedly selecting the Al-Nassr forward.
In the wake of defeat, Martinez confirmed his own departure after three and a half years in charge during which he led Portugal to Nations League success last summer.
"It's true that this is my last game for Portugal," he said post-match, adding Ronaldo had been "an exemplary captain".
"I arrived when there was a lot of confusion and questions in terms of his position in the team.
"But he has been an example not only in the number of goals he has scored, but also in the counter-attacks he leads. He is an example, a role model to follow. He is a football icon. There aren't many Ronaldos out there."
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