In response to applications filed by the Romanian Gymnastics Federation and gymnasts Ana Maria Barbosu and Sabrina Maneca-Voinea, CAS ruled that the appeal of Chiles's degree of difficulty was submitted past the one-minute deadline for such inquiries and should not have been granted.
After the review, Chiles's score was upgraded to 13.766. That was enough to earn bronze behind Brazil's Rebeca Andrade and superstar US teammate Simone Biles.
But it was a devastating blow for Barbosu who thought she had bagged bronze with her score of 13.700.
Both she and Maneca-Voinea, who was pushed into fifth, departed the competition in tears.
Such scoring inquiries are regularly lodged during gymnastics competition, some are rejected and others are upheld, resulting in a change of score.
Romanian prime minister Marcel Ciolacu called it a "scandalous situation" and said he would boycott the Olympic closing ceremony.
The drama unfolded in the final event of gymnastics competition at Bercy Arena on Monday.
CAS said in its statement that its ruling applied to Chiles's score, which said should be reinstated at its original 13.666.
But CAS didn't rule on the final floor exercise ranking, saying the International Gymnastics Federation (FIG) will have to sort out the medals.
"The Federation Internationale de Gymnastique shall determine the ranking of the Final of the women's Floor exercise and assign the medal(s) in accordance with the above decision," CAS said.
USA Gymnastics and the United States Olympic and Paralympic Committee issued a joint statement saying they were "devastated" by the ruling.
"The inquiry into the difficulty value of Jordan Chiles's floor exercise routine was filed in good faith and, we believed, in accordance with FIG rules to ensure accurate scoring," the governing bodies said.
"Throughout the appeal process, Jordan has been subject to consistent, utterly baseless and extremely hurtful attacks on social media.
"No athlete should be subject to such treatment. We condemn the attacks and those who engage, support or instigate them.
"We commend Jordan for conducting herself with integrity both on and off the competition floor, and we continue to stand by and support her."
