Showered in confetti and flanked by sequined samba queens, Rio's mayor symbolically relinquished control of the city to its rotund Carnival king on Friday to kick off the five-day festivities, a time of joyous excess when the streets fill with roving percussion bands and throngs of dancing, drinking revelers.
The city is primed for the madness, with a hot tropical sun shining through a clear blue sky onto the backs of hundreds of thousands of partygoers who've taken over the streets, joining one of the traditional "bloco" parties that march behind a band playing old samba tunes.
"I am giving over a city at the height of its rebirth," said Mayor Eduardo Paes, handing the key to the city to Milton Junior, who is serving this year as King Momo, the mythical jester who reigns over the extravaganza.
Rio's star is rising of late, as the city prepares to host the final matches of the 2014 World Cup and the 2016 Olympics, and this year's Carnival is forecast to be an even bigger blowout than usual, with 20 percent more tourists expected than in 2011.
Rio officials say they're also better prepared to keep the chaos under some semblance of control, with more portable toilets, traffic guards and paramedics, as well as a new central command center monitoring it all.
"It's a matter of organization and comfort; we're thinking of the partiers, but also of the residents," said the president of Rio's tourism department, Antonio Figueira de Mello, adding that the city will welcome 3 million visitors this summer, about 850,000 of them during the raucous free-for-all.
The celebration has proved immune to the crisis devastating economies in Europe and the U.S., said Mello. "There is no crisis that can take down Carnival."
The festivities also signal a return to normality for Rio and Salvador, the capital of the northeastern state of Bahia, after police strikes raised fears that the parties might be ruined by rampant crime. In Salvador, which hosts Brazil's second-largest Carnival and arguably its wildest, the strike led to a spike in murders earlier this month. Rio's short-lived work stoppage was peaceful, and ended last week with minimal disruption.
As of Friday afternoon, neither city reported any serious problems as the parties began.
In Rio, merrymakers are expected to spend $640 million and generate 250,000 jobs, most temporary and in the tourism and services industries, during Carnival alone, according to the city's economic development department. But the world's biggest party traditionally leaves a hangover to match: last year, the romp left about 850 tons of trash strewn around town.
Rio officials have dispatched 80 mobile medical emergency units, 1,000 traffic guards and 15,000 toilets around the city, and officials are running a campaign against urinating in public. Rio residents are humming along with a catchy samba tune running on TV, telling partiers, "If you want to pee, don't do it here, don't do it here," which rhymes in Portuguese.
It wasn't yet clear if the city's organizing effort was paying off, at least for Fernando de Souza Maciel, a shirtless college student sweating into a pink tutu and ribboned ballet slippers who stopped to get a juice with friends between street parties in the Botafogo neighborhood.
"I can't say I haven't taken advantage of a street corner to find some relief after that third beer," he said, referring to past Carnivals. "But I promise I'll look for a toilet this year."
His two girlfriends sent up a cheer for Paes _ "Go mayor!" _ when asked about this year's plentiful toilets.
"It makes all the difference," said Mayara Marconi, whose butterfly wings were a little off-kilter from the jostle of the crowd. "It's a fine line between having fun and desperation, that moment where you'd trade your kingdom for a toilet."
For tech-savvy revelers, Rio launched a smartphone app, free for iPhones and Androids, that tells visitors in English, Spanish or Portuguese where to go for blocos, the mobile samba bands that draw millions, pied-piper style, through the streets, as well as basic information on public transit, eateries and museums.
Brazil's federal aviation authority expects 3 million people to shuttle in and out of airports during Carnival week, 13 percent more than last year. Airports taking in visitors will also have 30 percent more federal police, and workers with vests asking "May I help you?" will be circulating to take care of last-minute questions.
Helping the notoriously gridlocked city tackle the street closures, mass gatherings and parading parties is Rio's new central command center, which the city hopes will keep order when Rio hosts the 2014 World Cup matches and the 2016 Olympics.
It has been fully operational since November, but this is the first big test of its ability to keep the city running during a large event.
The center takes feeds from more than 500 cameras spread around the city and will help plot the routes of Rio's more than 400 roving street parties, along with the points were guards, medical units and toilets will be placed.
Center director Savio Franco said he hopes all this planning will make it a cinch to maintain control of Carnival.
"There will be more than 5,000 city government workers involved in making this party go as smoothly as possible for cariocas and for the tourists," Franco said.