Brazil's 'shameless' fans supporting Messi's Argentina
But since they were knocked out by Croatia in the quarter-finals, he switched allegiance to Brazil's arch rivals, Lionel Messi's Argentina.
"As a football fanatic I think Argentina deserve this title," said the 38-year-old odontologist upon his return to Sao Paulo.
He cheered on Argentina during their 3-0 semi-final victory over Croatia on Tuesday that saw the South Americans qualify for Sunday's final.
Dos Santos Junior even wears his light blue and white Argentina jersey "without shame" on the streets of Brazil's biggest city.
He will put aside eternal debates such as who was better between Brazil's Pele and Diego Maradona of Argentina to support the Albiceleste against France.
"Argentines are passionate about their teams and their national team, which has the bit between its teeth," he said. "Any football lover supports such a noble cause."
Earlier in the World Cup, Argentina coach Lionel Scaloni said that if his side could not win the tournament "I prefer that a South American team" does, even Brazil.
But while 33 percent of Brazilians identify Argentina as their "second" team, more than 60 percent say they wouldn't want their neighbor to win the World Cup, according to a poll by the Brazilian data analysis institute.
'Brazil cowered'
The relationship between Argentines and Brazilians is a complicated one when it comes to football.
After Argentina lost their opening World Cup match against outsiders Saudi Arabia, Brazilian social media was awash with jokes and memes, some playing on the famous "Don't Cry for me Argentina" song composed by British duo Andrew Lloyd Webber and Tim Rice and popularized in the musical Evita.
Yet it was Brazil crying first after they were knocked out.
Argentines also had the last laugh during the 2021 Copa America as Messi and his teammates beat their historic rivals 1-0 in the final in Brazil's Maracana fortress.
Videos circulating on social media even showed Argentina's players singing "Brazilian, what happened? The five-time champions cowered," in the changing rooms after Scaloni's team beat Croatia.
And yet some prominent Brazilian figures are right behind Argentina.
The great Pele, who won the World Cup three times with the Selecao, celebrated Argentina's semi-final victory and the genius of Messi from his hospital bed in Sao Paulo, where he was originally admitted in late November for cancer treatment.
His daughter Kelly published a social media post of Pele watching the match that included appreciative GIFs aimed at Messi.
"There are no words for you @leomessi," former attacking midfielder Rivaldo, a World Cup winner with Brazil in 2002, wrote on social media.
"God knows and he will crown you on Sunday, you deserve this title."
'Crazy for Messi'
Messi, 35, is widely regarded alongside Pele, Maradona and Portugal's Cristiano Ronaldo as one of the greatest players to ever grace the game.
And there is only one trophy missing from his incredible career: the World Cup.
Many Brazilians are as desperate to see him win it before he retires as they are to see their own hero Neymar, five years Messi's junior, do so.
"After Brazil were knocked out I started cheering for Argentina because Messi is the best player I have seen. He is playing at an impressive level and it's only right that he is crowned," said economist Alexandre Caldas, 49.
Caldas's eight-year-old son Bernardo is a huge Messi fan.
"He's crazy about Messi, he wants him to win, to be the best in the world and is even learning Spanish so he can ask for his autograph," said Caldas, who has bought his son an Argentina football kit.
However, for some people the neighborly rivalry trumps everything.
Brazil's former star striker Ronaldo, known as El Fenomeno (the phenomenon) during his career and who won the World Cup alongside Rivaldo, has picked France as favorites on Sunday.
And while he says he would be happy for Messi to win the World Cup, he added: "I'm not going to be so hypocritical as to say I would be happy for Argentina."
