Oscar will be wearing the No. 10 jersey made famous by Pele and will be in charge of leading the midfield during the London Games.
The 20-year-old who calls himself the "modern playmaker" has become the latest young Brazilian to make a move to European football, joining the European champions as soon as the Olympics are over.
The expectations about Oscar are so high in Brazil that he is seen as one of the players guaranteed to be on the team which will try to win the World Cup at home in 2014.
Official details on Oscar's transfer from Brazilian club Internacional to Chelsea were not made available, but reports in England and Brazil say it was worth 25 million pounds (nearly $40 million), making it the highest transfer of a player leaving Brazilian football, surpassing those of Robinho to Real Madrid in 2005 and Nilmar to Villarreal in 2009.
"I'm very proud to be able to wear Brazil's No. 10 jersey," Oscar said. "It's a jersey that has belonged to so many great players like Pele, Zico, Rivaldo."
Chelsea fans can expect to see an agile playmaker who has the skills to dribble and the vision to set up his teammates, a midfielder who likes to play straight toward the goal but knows how to mark when needed.
"Today, the player wearing the No. 10 jersey has to run a lot and look for spaces to get plays going," Oscar said. "You have to defend a lot and be always fighting for ball possession. It's different from the traditional No. 10 from the past."
He showed his skills in Brazil's 3-2 win over Egypt in the team's Olympic opener on Thursday, setting up two goals. It was his first match since Chelsea announced his signing on Wednesday.
"I'm incredibly happy to be moving to a great team like Chelsea," he said. "It's a great opportunity in my career and I think I'll enjoy it."
Oscar, whose full name is Oscar dos Santos Emboaba Junior, appeared as a promising star while playing for Sao Paulo and quickly made his way to Brazil's youth squads. He has played at every level of international football from under-15.
He had an important role when Brazil won the 2011 South American Under-20 tournament in Peru, helping give Brazil a spot at this year's Olympics. He was even more crucial in last year's Under-20 World Cup in Colombia, scoring all three Brazil goals in the 3-2 victory over Portugal in the final.
But a few months ago Oscar was in danger of not even making it to the Olympic squad because of a judicial dispute involving his former clubs Internacional and Sao Paulo, which sued Internacional, accusing the club of illegally signing the youngster at the end of 2010. The dispute forced Oscar to miss a few games pending a court decision.
Brazil coach Mano Menezes hinted at the time that Oscar likely would be left out of the Olympic squad if his situation wasn't resolved quickly and if he didn't get to play soon.
Sao Paulo and Internacional eventually reached an agreement and Oscar made the squad as expected, but his condition as a starter wasn't secured until after a series of friendlies before the Olympics.
Santos playmaker Paulo Henrique Ganso was widely seen as the one in charge of Brazil's midfield, but injuries and performances below expectations allowed Oscar to quickly gain the respect and the confidence from Menezes, as well as from Brazilian fans and media.
"I'm sure that I guaranteed my spot as a starter after what I did in the friendlies, I know that I played very well during those matches," Oscar said.
He has already gained praise from Chelsea coach Roberto Di Matteo, but he will have to fight for a spot in the starting lineup with other new signings such as Eden Hazard and Marko Marin.
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