Itaquerao Stadium shined under blue skies as Brazil kicked off its home World Cup with a football-style Carnival Thursday before thousands of dancing yellow-clad fans, who seemed eager to put construction delays and protests behind them.

Jennifer Lopez, rapper Pitbull and pop star Claudia Leitte bounced around a giant stage resembling a peeled melon singing the World Cup theme "We Are One" as Brazilian band Olodum banged drums below on this nation's Valentine's Day.

JLo, dressed in a low-cut sparkling green outfit, turned up for the performance despite earlier reports that she wouldn't be able to attend.

Brazil is ready to samba, and plans to teach the world to join in for the coming month during the showcase tournament for the world's most popular sport. The futebol-crazed country hoped Thursday's Croatia-Brazil opener would be the start of a run to extend its record to six World Cup titles.

At one point at the end of the ceremony, fans chanted and booed against Brazilian President Dilma Rousseff and soccer's governing body, FIFA. Many in the nation have complained that spending on the World Cup and the 2016 Rio Olympics has diverted cash from the poor and infrastructure improvements.

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Jennifer Lopez, left, Claudia Leitte, centre, and Pitbull perform during the FIFA World Cup opening ceremony in Sao Paulo, Brazil. (Kirsty Wigglesworth/Associated Press)

Although traffic and transit strikes have plagued the sprawling Sao Paulo area in recent weeks, thousands made it into Itaquerao Stadium in plenty of time to party. The home fans cheered alongside small pockets of spirited Croatians in their checkered red and white tops.

The field was covered in multi-colored rays for the opening ceremony, which cost 18 million Brazilian reais, or about $8 million. A stadium worker died March 29 while installing temporary seats for the opener after construction already had been behind schedule.

Video highlights and memorable bloopers from past World Cups were shown on the big screens at either end of the stadium toward the conclusion of the 30-minute show. The program was choreographed by Paulo Barros, a two-time winner of the samba school title at the Carnival in Rio de Janeiro. After 100 hours of rehearsal and 31 auditions, circus artists and army soldiers were among those who performed.

Protesters, police clash

Nearly half the world's population, well over three billion spectators, is expected to watch soccer's premier event and get a glimpse of the country that in two years will host the Summer Olympics.

Play began with Brazil and Croatia meeting in Sao Paulo on Thursday. Brazilians are hungry to see their soccer juggernaut deliver a record sixth World Cup crown to a nation desiring something — anything — to celebrate after enduring a year of gruelling protests and strikes.

But as play begins, it still isn't clear which Brazil we'll see.

Will it be the irreverent nation known for its festive, free-wheeling spirit? Or the country that for the past year has been a hotbed of fury over poor public services, discontent over a political system widely viewed as corrupt and deep anger over the $11.5 billion US spent on hosting the World Cup?

By mid-morning, it looked like it would be both.

Protesters and Brazilian police clashed in Sao Paulo on Thursday, with more than 300 demonstrators gathered along a main highway leading to the stadium. Some in the crowd tried to block traffic, but police repeatedly pushed them back, firing canisters of tear gas and using stun grenades. 

A few protesters suffered injuries after being hit by rubber bullets, while others were seen choking after inhaling tear gas. An Associated Press photographer was injured in the leg after a stun grenade exploded near him. CNN reported on its website that two of its journalists were also injured. 

"I'm totally against the Cup," said protester Tameres Mota, a university student at the demonstration. "We're in a country where the money doesn't go to the community, and meanwhile we see all these millions spent on stadiums." 

About 300 protesters also gathered in central Rio de Janeiro in another demonstration against the World Cup, though no clashes were reported by early afternoon.

Meanwhile, the streets were filled with fans ready for festivities.

"The world is going to see multitudes cheering for soccer — but also demanding that our country change," Helen Santos, a school teacher, said as she walked home in Rio de Janeiro.

"The world needs to see that we're a serious country. We're not just a nation of soccer, but a country striving and demanding the government provide better education and health care.

"The world needs to see the reality of Brazil, not just the sport."

'What will the world see?'

Street protests have lessened in size since last year when Brazilians staged raucous rallies against the government, overshadowing the Confederations Cup soccer tournament. On one night, about a million people spontaneously spilled into the streets of various cities. For two weeks, dozens of places were roiled by unrest.

"I hope the soccer outshines the protests, but I also know there remains a climate of anger," said Edson Carvalho, an office assistant watching 10 barefoot young men play a pick-up soccer match in Rio's Botafogo neighbourhood.

"What will the world see? I'm waiting to find out myself."

In 2007, when FIFA named Brazil as the host nation for the 2014 World Cup, the country's folksy and immensely popular president at the time, Luiz Inacio Lula da Silva, told a celebratory gathering in Zurich he would return home filled with joy, but also feeling the burden that comes with hosting the world's biggest sporting event.

"At the heart of the matter, we're here assuming as a nation, as the Brazilian state, to prove to the world ... that we're one of those nations that has achieved stability," Silva said then. "Yes, we're a country that has many problems, but we're a nation with men determined to resolve those problems."

Silva added that he "wanted to assure FIFA officials" that Brazil would prove able to put on a great Cup.

Seven years on, as the global spotlight finally shines on Brazil, the world will see a great sporting event with soccer returning to one of its most passionate cores on a continent that relishes the game.

But the glare also will glow on those problems Silva referred to, the lingering ills that have not gone away

With files from CBC News