In the following moments, the crown was removed and placed on the head of a mystified Pia Alonzo Wurtzbach of the Philippines, other contestants rushed to console Ariadna Gutierrez Arevalo of Colombia and a sheepish Harvey felt compelled to apologize on Twitter and to reporters assembled backstage.
"I feel horrible for this young woman," he said.
Harvey said it was his mistake and that he would take responsibility for not correctly reading the card, which said that Wurtzbach was this year's winner and Colombia was actually the first runner-up.
He held up the card for Fox network cameras to see up close afterward. Talking with reporters afterward, Harvey and an executive for pageant owner WME-IMG called it human error.
"Nobody feels worse about this than me," he said.
Here's video showing the mishap:
Wurtzbach appeared stunned as she walked to the front of the stage alongside the crown-wearing Arevalo before last year's Miss Universe from Colombia removed the crown and placed it on Wurtzbach's head.
RELATED: The funniest reactions to Steve Harvey announcing the wrong Miss Universe winner
Wurtzbach later said she felt conflicting emotions as the mistake happened: joy when she was told she had indeed won, concern for Colombia contestant Ariadna Gutierrez Aravelo and confusion at the whole situation.
Wurtzbach said she tried to approach Aravelo onstage afterward, but the Colombian was crying and surrounded by a crowd of women. She said she realized it was, "probably bad timing."
"I did not take the crown from her," Wurtzbach told reporters after the pageant concluded, saying she wished the contestant from Colombia well and hoped the Latin American community understands that "none of this was my fault."
"None of this was done on purpose. It was an honest mistake," she said, apologizing on behalf of the organization she now represents. She said Harvey told her afterward that she "should just enjoy the moment."
Harvey also apologized on Twitter, but at first misspelled the home countries of both contestants before also fixing that. "I'd like to apologize wholeheartedly to Miss Colombia & Miss Philippines for my huge mistake," he wrote. "I feel terrible."
Harvey, who was hosting the contest for the first time, said he re-read the card and noticed it said "first runner-up" next to the Colombia contestant's name before he asked producers if he had made a mistake.
An executive with pageant owner WME-IMG, Mark Shapiro, said Harvey caught the mistake and corrected it on his own, saying he wanted to make a wrong into a right.
"It was humiliating for the women. It was humiliating for him," he told reporters after the pageant.
As all this was unfolding, a car drove up onto a sidewalk and struck dozens of people just outside the Planet Hollywood hotel-casino where the pageant was taking place. The Las Vegas Strip was soon jammed with ambulances and fire trucks, and authorities said at least 30 people were taken to a hospital to be treated for injuries and one person was killed.
Even before Sunday night's oops moment, the pageant was involved in another controversy when a backlash against the pageant's former owner Donald Trump led Univision to pull out of the broadcast and the businessman to sell it in September.
The competition started with women representing 80 countries between the ages of 19 and 27. For the first time, viewers at home weighed in, with their votes being tallied in addition to four in-person celebrity judges.
NBCUniversal and Donald Trump co-owned the Miss Universe Organization until earlier this year. The real-estate developer offended Hispanics in June when he made anti-immigrant remarks in announcing his Republican presidential run.
That led Spanish-language network Univision to pull out of the broadcast for what would have been the first of five years airing the pageants and NBC to cut business ties with Trump.
The former star of the "Celebrity Apprentice" reality show sued both companies, settling with NBC in September, which included buying the network's stake in the pageants.
That same month, Trump sold the organization that includes the Miss Universe, Miss USA and Miss Teen USA pageants to entertainment company WME-IMG.
Shortly after Sunday night's confusion, Colombian President Juan Manuel Santos tweeted a message on his official account to Ariadna Gutierrez. "For us, you will continue being miss universe! We are very proud!"
Philippines presidential spokesman Edwin Lacierda didn't address the controversial win but said, "in bagging this victory, Ms. Wurtzbach not only serves as a tremendous source of pride for our people, but also holds up the banner of our women and of our country-as a true representative of what the Filipina can achieve."
It's the third time a contestant from the Philippines has won the title. It could have been the second win in a row for Colombia.
The pageant's contestant from the United States, Olivia Jordan, was named second runner-up.