In a vote of high drama, the bustling Brazilian carnival city of beaches, mountains and samba beat surprise finalist Madrid, which got a big helping hand from a very influential friend.
Chicago was knocked out in the first round - in one of the most shocking defeats ever handed down by the International Olympic Committee. President Barack Obama's last-minute hop to Denmark didn't swing the games Chicago's way. He came, saw, charmed but did not conquer.
Even Tokyo, which trailed throughout the tight race, did better - eliminated after Chicago in the second round. On Rio's Copacabana beach, where the city will hold beach volleyball in 2016, the party was heading into the night. In Chicago,.
Rio spoke to IOC members' consciences: the city argued that it was simply unfair that South America has never hosted the games, while Europe, Asia and North America have done so repeatedly.
"It is a time to address this imbalance," Brazil's charismatic president, Luiz Inacio Lula da Silva, told the IOC's members before they delivered their verdict. "It is time to light the Olympic cauldron in a tropical country."
As the four cities began their final presentations, analysts say at least 25 of the 101 delegates had not made up their minds who they would vote for, reports CBS News correspondent Sheila MacVicar from Copenhagen.
The final result was decisive: Rio beat Madrid by 66 votes to 32. Chicago got just 18 votes in the first round, with Tokyo squeezing into the second round with 22. Madrid was leading after the first round with 28 votes, while Rio had 26.
In the second round, Tokyo was eliminated with just 20 votes. Madrid got 29, qualifying it for the final round face-off with Rio, which by then already had a strong lead, with 46 votes.
Beating three rich, more developed nations that had all previously held the games represented a giant, morale-boosting coup for Brazil, an emerging nation bounding up the ranks of the world's biggest economies but which still has millions of people living in poverty. Rio is known as much for its crime-ridden slums as for its stunning natural beauty.
Silva, a bearded former union leader, disappeared into a huge group hug with the joyous Rio team after IOC president Jacques Rogge announced the city's name. Football great Pele had tears in his eyes. Silva wept into a white handkerchief at a post-victory news conference. Brazil will now hold the world's two biggest sporting events in the space of just two years: in 2014, it is organizing the World Cup.
The slap to Chicago was such that some IOC members were left squirming. The city's plans for Olympic competition along its stunning Lake Michigan waterfront had long made it a front-runner and earned support from the highest possible level - Mr. Obama himself. His wife, Michelle, flew in two days before the vote to butter up IOC members, an essential part of the selection process. And Mr. Obama himself flew in Friday morning.
IOC members had seemed wowed, posing for photos with Mrs. Obama and taking souvenir shots of the president with their mobile phones. But, in the vote, Chicago was shunned.
"Either it was tactical voting, or a lot of people decided not to vote for Chicago whatever happened," IOC member Gerhard Heiberg said. "Nobody knows, but everybody is in a state of shock. Nobody believes it. I'm very sorry about it."
Some delegates said they were less than impressed that Mr. Obama stayed just four hours - and left before the voting even began, reports MacVicar.
Sources familiar with the Olympic committee told CBS News Chicago focused too much on celebrity at the expense of what the city has to offer.
It's estimated close to $70 million had been spent already on Chicago's Olympic campaign, reports CBS News correspondent Dean Reynolds. Private money was to pay for the games themselves during which the city would maximize its lakefront locale and its existing facilities while hoping to contain an epidemic of violence that has shaken many neighborhoods.
Rio's bid, while high on romance, is not without risk. Because of Rio's high crime and murder rates, security will be a constant issue in 2016. Preparing Rio for the Olympics will cost billions of dollars - money that critics said could have been better spent on tackling the city's social problems.
But the lure of that untapped frontier proved too strong for the IOC.
"There was absolutely no flaw in the bid," Rogge said.
Added Heiberg: "We have sent out a message that we want to go global."
Now, Africa and Antarctica are the only continents never to have been awarded an Olympics.
Madrid's surprising success in reaching the final round came after former IOC president Juan Antonio Samaranch made an unusual appeal for the Spanish capital, reminding the IOC's members as he asked for their vote that, at age 89, "I am very near the end of my time."
Samaranch ran the IOC for 21 years before Rogge took over in 2001.
Mr. Obama himself only spent a few hours in the Danish capital and left before the result was announced.
Former IOC member Kai Holm said the short stopover was "too business-like," Holm said. "It can be that some IOC members see it as a lack of respect."
Senior Australian IOC member Kevan Gosper surmised that Asian voters may have banded together for Tokyo in the first round, at Chicago's expense.
"I'm shocked," Gosper said. "The whole thing doesn't make sense other than there has been a stupid bloc vote."
He worried that the shock exit could do "untold damage" to the already testy relations between the IOC and the U.S. Olympic Committee. They had recent flare-ups over revenue sharing and a USOC TV network.
"To have the president of the United States and his wife personally appear, then this should happen in the first round is awful and totally undeserving," Gosper said.
Added Dennis Oswald, another member: "It was a defeat for the USOC, not for Chicago."
The biggest bloc of voters on the IOC - 46 - are Europeans. The IOC's last two experiences in the United States were bad: the 2002 Salt Lake City Winter Olympics were sullied by a bribery scandal and logistical problems and a bombing hit the 1996 Games in Atlanta.
Mr. Obama had held out the enticing prospect of a Chicago games helping to reconnect the United States with the world after the presidency of George W. Bush. He told the IOC earlier Friday that the "full force of the White House" would be applied so "visitors from all around the world feel welcome and will come away with a sense of the incredible diversity of the American people."
Now, Chicago can only rue what might have been. And Mr. Obama's gamble of expending his own political capital on the bid failed.
"He didn't do too much," French IOC member Guy Drut said.
He said that the USOC's financial disputes with the IOC were still unresolved. And he said White House security unnerved some IOC members.
"This morning the city was closed because of Barack Obama," Drut said.
The last U.S. city to bid for the Summer Games, New York, did scarcely better. It was ousted in the second round in the 2005 vote that gave the 2012 Games to London.
Tokyo did better than many expected by reaching the second round. It had offered reassurances of financial security, with $4 billion already banked for the games. But the fact that the Olympics were held only last year in Asia, in Beijing, handicapped the Japanese capital's bid.