The four-week feast of football in the sport's spiritual homeland gets under way in Sao Paulo, where Brazil face Croatia at 5pm or 3am on Friday in Thailand.
The start of the four-yearly extravaganza is the acid test for organisers and football's governing body FIFA, who have been scrambling to get Brazil ready for the biggest single sport event.
The first of 64 matches which culminate with the July 13 final in Rio de Janeiro will be staged in the Corinthians Arena, a symbol of the chaotic build-up.
Rousseff acknowledged that organizing the cup was tough, but she insisted that the 12 stadiums are ready and told foreign fans Brazil would welcome them with "open arms" like Rio's Christ the Redeemer statue.
"Brazil overcame the main obstacles and is ready on and off the pitch for the cup," she said in a nationally televised address late Tuesday.
Rousseff said she understood the protesters but insisted they are wrong.
"For any country, organizing a cup is like playing a game, sweating and often suffering, with the possibility of extra-time and penalty kicks," Rousseff said. "But the final result and celebration are worth the effort."
Construction of the $424 million (313m euros) 61,600 Sao Paulo venue ground to a halt in November when a giant crane toppled over and killed two workers. A third labourer died in an accident in March. Eight workers have died while racing to complete World Cup-related projects.
The 12 World Cup stadiums were due to be ready by the end of December. Six missed the initial deadline.
Only this week, workers could be seen busily wiping seats, checking beams and installing wiring just days before the opener, which will be attended by 12 heads of state, UN Secretary General Ban Ki-Moon and assorted VIPs.
- Blatter 'confident' -
Yet FIFA officials are bullishly backing Brazil, with President Sepp Blatter, under-fire over his handling of corruption allegations against Qatar's 2022 World Cup bid, strongly backing the hosts.
"We at FIFA, we are confident, it will be a celebration," said Blatter. "After the tournament kicks off I think there will be a better mood."
But the spectre of social unrest and transport chaos looms large.
A wage strike by Sao Paulo subway workers last week brought the city to a standstill, and led to riot police firing teargas to break up protesters before the walkout was suspended on Monday.
Union leaders have threatened to resume the strike during the tournament if their demands are not met. On Tuesday, subway workers in Rio de Janeiro, which hosts seven games including the final, threatened similar action.
Authorities worry about a repeat of nationwide protests around the FIFA Confederations Cup last year.
The estimated $11 billion Brazil is spending on the World Cup tournament has angered many in a country with chronically under-funded health and public services and violent crime.
The rapid spread of last year's protests caught Brazilian authorities off-guard, and a massive security blanket will be draped across the World Cup in an effort to avoid a repeat of the clashes.
Around 150,000 police and soldiers and some 20,000 private security officers will be deployed across the 12 host venues to counter protesters whose slogan is "the Cup will not take place."
In April, Rio's famous Copacabana district witnessed violent clashes after residents of a nearby favela accused police of shooting dead a local man.
And resentment at the vast amounts lavished on the tournament -- Brazil is believed to be the most expensive World Cup in history -- remains.
Brazil's footballers were targeted by striking teachers as they set off for their training camp outside Rio last month.
"An educator is worth more than Neymar," teachers chanted, referring to the team's star striker.
- A classic in store? -
Despite the off-field problems, the tournament itself promises to be a classic.
From dramatic backdrops such as Rio de Janeiro's famed Sugarloaf Mountain to Manaus in the heart of the Amazon, the World Cup promises to showcase the vast diversity of Brazil.
Defending champions Spain are bidding to make history by becoming the first side from Europe to win a World Cup in South America.
Vicente del Bosque's side have dominated international football for the past six years, winning two consecutive European championships either side of their memorable triumph at the 2010 World Cup.
Brazil, chasing a record sixth World Cup, host the tournament for the first time since their loss to Uruguay in the climax of the 1950 finals, when their neighbours inflicted a defeat which became a national trauma.
Brazil will look to the skills of striker Neymar -- player of the tournament at the Confederations Cup last year -- to provide the attacking flair.
If Neymar shines, the tournament could become a duel between him and his Barcelona team-mate, Lionel Messi.
The Argentine maestro has had a quiet year by his standards, losing his FIFA Ballon D'Or crown to Portugal's Cristiano Ronaldo, in an injury-hit season.
But Messi has excelled in the famous blue-and-white shirt since being handed the captaincy by coach Alejandro Sabella, and will be aiming to erase the memory of a disappointing 2010 tournament.
Argentina and Brazil could meet in the July 13 final at the refurbished Maracana Stadium, if the European challenge led by Spain falters.