He is small in stature and slightly built, but Neymar showed he can carry the hopes of a troubled nation with an electrifying performance in Brazil's World Cup opener.

With pressure piled on his young shoulders it would have been easy for Neymar to crumble, but instead the 22-year-old seized the moment with two goals in the 3-1 win over Croatia.

Helped by a large slice of luck, Neymar's dragged shot in the first half bounced in off the post. In the second half, he struck on a soft penalty kick that eluded Croatia goalkeeper Stipe Pletikosa.

Those details, as well as the fact the penalty was highly debatable, did not trouble the 60,000-plus crowd that erupted in delight as fireworks lit the skies outside the stadium.

"This is a dream come true, much more than I imagined," Neymar said afterward. "But more important than anything is that our team won."

Given the situation in Brazil, with ambivalence towards the World Cup and police tear-gassing protesters in Sao Paulo just hours earlier, the value of those goals could be high.

When President Dilma Rousseff was seen on the big screen celebrating Neymar's second goal, the crowd responded with a foul-mouthed chant.

Protests around the country over the World Cup's huge price have put a question mark over whether the tournament would be a success, despite the fact it is being played in soccer's spiritual home.

Neymar is Brazil's undisputed star, adored for repeatedly snubbing European clubs before joining Barcelona and promoted so efficiently the phenomenon is known as "Neymarketing".

He played like he had a point to prove, using his quick footwork to beat defenders and putting in a dangerous cross that could have brought the opening goal.

Brazil went down 1-0 on an own goal by Marcelo in the 11th minute, and when Neymar was booked for a yellow card near the half-hour it looked like the evening might finish disastrously for the host.

But almost immediately, Oscar found Neymar with space to run and his left-foot shot, despite not being cleanly hit, was accurate enough to beat a diving Pletikosa.

When Fred won a controversial penalty in the second half, Neymar got his second goal despite theatrically checking his run-up and hitting a shot well within the goalkeeper's reach.

After the match, wearing a baseball cap, earrings and bright green backpack, he gave thanks for the crowd support, which included a spine-tingling rendition of the national anthem.

"I have to give congratulations for the support, it motivated us a lot. They kept us going the whole time, and we needed it," Neymar said.